TL;DR: Buying these types of units in the dead of winter sucks. But kudos to heating mats for expediting the thaw. So far so good though - a worthwhile upgrade over the DELTA Pro.
As noted elsewhere, we bought three DELTA Pro 3 units from eBay during EcoFlow's amazing sale ($1800 each!) to replace our loyal DELTA Pro pair and bump capacity up to 36kWh max, more than enough to run the entire circuit load except in extreme heat/cold situations which is generally only a few days a year.
Being able to reuse the DELTA Pro Extra Batteries was ultimately the big decider - the Ultra had a great deal as well but just not as flexible as an upgrade. We also didn't favor lugging the Ultra components down frightening stairs.
FedEx was and is having major logistical issues - short answer: it took almost two weeks to get the devices and the third was delayed despite only being two states away. The root of the FedEx crunch seems to be Illinois.
Colorful boxes, like the good old days.
Despite being boxed up and "powered off", the EcoFlow app immediately recognized and offered to add them (which we declined).
Despite the eBay ad indicating that accessories might be missing, everything was present and accounted for - even the leather handle wraps and booklets, boxed up neatly. There were no obvious damage or dirt indications on the units barring minor scuffs on the top. One of them even had the stickers on the buttons that come when they're new. Whoever had them before us either didn't have them long or EcoFlow does a masterful job at restoring them to near new status.
In other words: if you're hesitant about the eBay EcoFlow route due to concerns about the unit, at least in our case, those concerns are unfounded and the prices are excellent especially now.
That "Early Christmas" feeling.
At 125lb each these aren't light units, but the wheels made them somewhat easier to take down and place. And they were indeed freezing cold (the unit throws Error 012 which is an undertemperature warning); we wrapped them in a heating mat.
One of them took longer than the other, but it basically took roughly 3-4 hours total before we could get them warm enough to even start charging - and that's with a heating mat. Then the charging was initially slow - 1.2kWh initially, then slowly fluctuating between that and the expected 4kWh until it got over 95%. This was unexpected - and we can't tell if it's expected behavior, a byproduct of residual internal cold or a defect. The DELTA Pros were never subjected to such cold so we have no point of comparison; they always charged at 3.6kWh until 95%.
But basically (due to winter cold snap), a minimum of 5 hours from dropoff to fully usable status.
And then...the Panel (2).
Of pleasant surprise was how seamless and smooth the Smart Home Panel 2 experience was.
We made sure to add the units to the same Space that the Panel resided in (not plugged into the Panel), got the firmware up to date (and they were quite a bit out-of-date), then plugged up to the Panel AC's and waited for them to warm up.
Beyond that there was none of the frustration seen with the DELTA Pro; the Pro 3 units just worked right out the gate and the DELTA Pro Extra Batteries were immediately recognized (they were already full).
We tested discharge, and it went just as smoothly. In fact, we never heard the "clunk" that the Panel would make with the Pro Hub when switching the relay over. Eagerly anticipating a superior discharge experience, we weren't disappointed: each Pro 3 took basically half of the total circuit load. No more of the unbalanced discharging that the Pro Hub had to do with L1/L2 split phase; they handled a 6kW rush of need without a problem. With the regular DELTA Pro, one of the "legs" would have been hammered more than the other, causing an unbalance that would result in an early halt to discharge.
Side note: If you're considering or have Extra Batteries for these Pro models, we highly recommend the superior flex battery cables. It's a night-and-day experience vs. the ones that come in the box. Might also work with the newer "3 Series" but can't confirm that.
At one point we got tempted to just test connecting a DELTA Pro 3 with the DELTA Pro / Hub connection...but chickened out at the last minute.
The technological evolution is clear.
The DELTA Pro 3 is clearly superior to the DELTA Pro in so many ways. It's whisper quiet even under heavy load (charging or discharging), it's more attractive to the eye, it has more connection flexibility, it doesn't require a Hub to connect to the Panel, etc.
But it also does subtle things. For example, when cycling through the various charging speeds we mentioned, the unit would beep to let us know. Also, when viewing each unit in the Space, the physical unit would beep. This is a small thing but powerful: the reason we named the Pros 'Izquierdo' and 'Derecho' is so we could identify which unit was which. The beep helps do that without the name (but we still went with 'Izquierdo 3' and 'Derecho 3' just for consistency. Third will have to be Centro.)
Not too sure about that Charge Priority though.
We're not used to this setting and frankly, it feels too restrictive as currently designed.
The specific setting is 'Charge & discharge order', and the idea is that you can tell the unit how to determine the order of consumption. The problem is, the only two options you get are (basically):
(A) you're smart DELTA Pro 3, you decide. OR
(B) always drain your own battery before draining the Extra Batteries.
Option A is the issue. From our testing, the behavior when fully charged is basically the same as Option B. There's no option that does what we think makes better sense, which is to draw equally across all available battery capacity at the same time. Why does that make better sense? Well, think about it this way.
If the main battery gets depleted, the Extra Batteries are of no use - which seems to make it illogical to just focus on the main battery and let it get the brunt of it until some arbitrary threshold is met or passed. If you're taking in 3kW of draw, wouldn't it make better sense to spread that out across three batteries vs. depleting them one at a time? Maybe.
On the other hand, if the Extra Battery could be designated as first draw source, it would allow you to take one and recharge it one-off via the Generator or another compatible EcoFlow unit to preserve the base charge of the main unit, if you got into a pinch.
Summary
DELTA Pro 3 is easily the finest overall device in the lineup, bar none, and its discount price is well worth it to get the most well-rounded possible unless your sole focus is capacity/runtime.