I specifically reached out to Tenvis official company support to find out exactly which firmware is the latest for my specific camera (this was just about 3 days ago), and they said it’s the one I have now (which is 1.2.1.4).
One problem with Tenvis cameras (and with this one in particular) is that they are inconsistent (and at the same time, indiscriminate) with their naming conventions, etc (well, it appears they don’t actually have any conventions; they just name things whatever they feel at the moment).
Example 1 = This camera (the IPROBOT3 that I own) now goes by at least two different names.
When I go to THIS URL on Amazon, it tells me that I purchased this camera back in 2014 (so, this page IS where I bought my IPROBOT3). However, the one I bought was actually named IPROBOT3 then, whereas they have changed its name (both here on Amazon as well as on their own website) to TZ100. No big deal; one just needs to keep different product names in mind for exactly the same product.
Example 2 = This camera NAME (IPROBOT3) has been used by Tenvis for at least two completely different cameras.
There was another camera by them that uses a completely different firmware line (and different numbers), but has exactly the same name as mine. If I were to attempt to upload the firmware for the older IPROBOT3 camera to mine, it would most certainly break it.
Unless somebody else can somehow prove to me that they have exactly the same camera model as mine, there’s no way I will attempt putting firmware on it that Tenvis support tells me will brick it.
So, is there any chance that anybody that has a Tenvis IPROBOT3 working with this DH would be willing to help me out? In order to know for sure which actual camera model you have, I will need to see photographs of the device itself (from all angles), as well as screenshots (with appropriate blurring, etc, obviously) of all of the pages in the web admin control panel.
This way, I will be able to see for sure whether or not it’s actually the same product named IPROBOT3 (remember from above, Tenvis has at least two completely different cameras with this exact same name).
If you want to help out, please PM me. 
@RBoy
UPDATE: Thanks to @kimmi for the assist.
They sent me some photos of their IPROBOT3 camera as well as screenshots of the admin pages.
Unfortunately, it was exactly what I needed to figure this out, but not what I wanted. lol
As it turns out, their IPROBOT3 that IS working with this Device Handler is the earlier product that Tenvis named IPROBOT3 (referred to sometimes as the 2013 version) and mine is the later one (sometimes referred to as the 2014 version). Two completely different products that look exactly the same in almost every way, but they are on a completely different firmware line.
So, I guess perhaps the wording for this Device Handler, where the Tenvis IPROBOT3 is concerned can still say that it supports the Tenvis IPROBOT3, but it should also include a mention of the fact that it supports the 2013 product with that name, and not the 2014 one.
Thanks a lot for helping out on this. I really appreciate it!