@Sabrent I bought one!
Hotplug and hotswap seem to be fine. Seems like each bay is a separate USB device, unlike DS-4SSD. So, apparently it's a USB hub with five SATA controllers, without a SATA multiplexer. Which is actually good. UASP seems to be fine as well.
TRIM over USB seems to be disabled by default in Linux - for any device, not just this one - so that would require a little more configuration, but it's completely a Linux issue, not a device issue.
However, it is not on ASM1543. At least according to its identification, it's one of those:
ASM1051E SATA 6Gb/s bridge
ASM1053E SATA 6Gb/s bridge
ASM1153 SATA 3Gb/s bridge
ASM1153E SATA 6Gb/s bridge
I assume it's not the 3Gb/s one, so 1051/1053/1153. Unless you are that much into reflashing chips with non-native firmware. (I guess I would need to tear off the rubber feet to disassemble it, and I don't waht to do that.)
And you are into that indeed, because I also bought a EC-UASP, and that one is on our good old friend JMS578 that identifies as a JMS561U. (Disassembling it was very easy, and it's not a $150 product, so I did that to check the actual chip.) But at least it properly advertises TRIM this time, and does not have that "PRODUCT: Go to final lap" nonsense.
It even has a firmware updater available in "Support" section! This is what it looks like:
I guess I'm supposed to click the arrow?.. I'd like to, you know, see if my device is recognized, what version is it on now, what updates are available, all that stuff... Either way, clicking the arrow does nothing.
After a while, I realized that I am supposed to click a line of text that does not fit on my screen. That's all this huge window has to offer, and it can't even put the most important part at the top where it would be noticeable in any situation!
There are also links and the support number! But no, apparently a huge picture is more important.
Clicking that line of text downloads something for a second or two, and then shows this:
So... What happened? Did I get updated? From which version to which one? Which one of the connected devices got updated? I've done the whole procedure again to see if it will say anything like "You're already on the latest firmware", but no, it just "updated" me again exactly the same way.
Well, at least I don't think JMS578 is known for something like having the block translation logic wrong above 2 TB. Although who knows what's in this particular custom firmware, and I remember something about having to update them right away to fix that issue. But ASM1051E - the one that might be in DS-5R15 - does have exactly that issue, and there is no firmware update for that one.
Other than that, I've noticed that the new power supply for the 5-bay device is rated for 36W, and the older one for a 4-bay DS-4SSD is rated for 48W. Also, the new one has a very loud "coil whine". And both of them have a detachable connector in order to support different wall plugs, but they only come with an American plug with no options.
Also, the newer DS-5R15 does not have "flaps" to hold drives in place, so the drives sit very crooked. But I'd say this is actually good, because this way, there's more airflow around the HDDs that could get pretty hot and heat up any SSDs in the other slots. Especially since apparently the fan is trying to be "smart" - for some reason, it was not spinning right away, so I initially thought it was broken. But the fan is too loud as expected, so I'm just going to use it without the top part, and thus better airflow will really help.
The EC-UASP has only two imperfections: the latches will probably be very easy to break, since the case is not aluminium as I expected for some reason, and pulling the drive out is actually pretty hard without damaging either the SATA connector, or the latches, or your fingers. I intended to use it as a hot-swap bay, but if you use it normally, then any of that poses no problem. On the flipside, the Type-A cable connector is way better than anything else (except maybe Type-C - but I don't have much experience with Type-C yet), and the build quality is actually outstanding. Even if I do break the latches at some point, the drive is held perfectly even without the lid, and the cable connector seems very sturdy. The lid is also held in place very well, and there's even some soft padding to prevent the drive from moving around. Oh, and don't forget the power switch, which also looks like it won't break any time soon! And the activity LED behind that white panel! I don't think I've ever seen a better enclosure in terms of hardware design.
Most importantly, are those two products supposed to already have the latest firmware that fixes any kind of bugs like 2Tb+ support? Other than unclear and downright atrocious software practices, I'm actually very impressed with both products. And I guess the software part is like that because it usually "just works", so there's no need to fix it, and your focus is really on the hardware first and foremost.