Lacie was acquired by Seagate back in around 2012.
G-Technology was acquired by Hitachi (HGST) in 2009. HGST themselves were acquired by Western Digital in 2012, iirc.
Promise is still an independent brand last time I checked.
Both Lacie and G-Tech are kind of like the Lexus of their respective parent brands. So you pay more for the prettier design. You are also more likely be getting a faster 7200 RPM drive in comparison to what you would get in a budget offering from those brands. Promise is more of an "enterprisey" brand, but the Pegasus product line is aimed at the SOHO / self employed pro buyers.
Seagate and WD are the main manufacturers of hard drive disks these days. Both have had their bad batches over the years, but they are pretty much the same in overall reliability numbers.
I have an old Lacie 2Big (2 bay enclosure), a Promise Pegasus R4 (4 bay enclosure). Both of these are so old that I think that they may still be Thunderbolt 1. I also have an even older G-technology single 3.5" external drive with FW800, USB 2 and a drive that was made by HGST. All of them continue to work perfectly fine, but I have cut down my storage needs dramatically in the last two years, so only the Pegasus R4 sees regular use. The enclosures are unlikely to fail before the drives themselves do. Since you are looking at ones with removable drives, this is not a concern from my point of view.
In terms of support, I expect that for Lacie and G-tech it will mostly be fine, as one would expect from the likes of WD and Seagate anyway. Promise being a much smaller company may offer better, or worse support. I honestly do not know, because I have never needed support for any of these products.
Lacie and G-tech enclosures usually only offered software RAID, as far as I am aware, and the Promise Pegasus offers hardware raid. There are advantages and disadvantages to both approaches, which I won't go into here in details. One example of why hardware RAID is a disadvantage is that an enclosure requires a driver. When the M1 Macs came out initially the Pegasus products could no longer be used. Promise have now created a new driver, so that it's usable, but it took a few weeks. Also, the original Pegasus (the one I own) is considered "obsolete" by the company and no longer officially supported. It has not been validated with the AS driver, like the subsequent enclosures have been, but according to Promise staff on their forums the original Pegasus should work with this new driver anyway. I have not tested it, because it's permanently connected to my trashcan pro. This sucks a bit, but what can one expect from a product that is around 8 or 9 years old. <shrug>
