Wow, that sounds like the worst UPC I've ever seen or heard of. UTLRA is nothing but a budget brand and I would never recommend their products for mission critical uses or for protecting sensitive hardware. I've seen them take to many shortcuts on their line of PSU's to ever use them for anything I'd be upset to lose. To address your points:
1) The heat produced by the unit partly has to do with how efficient the unit is at converting AC to DC, it sounds like ULTRA does not use high efficiency components and/or doesn't provide sufficient cooling for them. Even when not charging the battery the unit should be conditioning the incoming power, although the implementation on ULTRA's seems to be basic.
2) I've owned APC, Tripplite, and Belkin UPS devices, I don't recall any smell to them except for a new factory (plastic) smell my latest APC unit had for the initial few minutes after I unwrapped it.
3) Out of all four models and three brands of UPS devices,
none of them power off when there is zero load on them. That sounds suspicious, do all of the units you puchased do this? For that matter, does more than one jump from 100% to 75% capacity on you?
4) After checking the review: regarding the power shutdown software, ULTRA does offer the ability to base the PC shutdown on the capacity of the UPS as well, so I don't see any problem with them offering the extra time-based system shutdown options.
The VA rating on a UPS does not actually tell the capacity of the unit, it's just a voltage-ampere rating. Specifically, I've seen 1500VA units rated for barely over 800W loads, and still other 1500VA units rated for 930W loads for the same amount of time. The VA rating is like using the wattage rating to judge what speaker system is better... it doesn't actually tell the consumer anything by itself. Just look at the wattage ratings for various 1500VA units and they can range wildly. Basically, just like many PSU manufacturers this number gets played with.
First, that unit itself states it requires 6 hours to recharge the battery to 90% right on the box, so obviously if the software claims it charged 50% capacity in 10 minutes then their software readouts are pretty inaccurate and nearly uselessly so at that.
Ontop of that, LR's testing claims it took 14.5 hours instead of 6 hours to recharge to 89%. Considering APC states my smaller 1500VA unit requires 16 hours to recharge, obviously ULTRA is fudging quite a few of their numbers...
Regarding the software indicating a near instant 100% to 75% capacity, it sounds again like a software issue. Legit Reviews observed the exact same behavior with their test unit:
http://www.legitreviews.com/article/367/6/
LR tested their 2000VA unit with a
192W load and got 35 minutes of battery life on it. This is a small load for such a large unit. I set up an identical computer+monitor 192W load on my APC 1500VA unit and got 28 minutes of run time.