To fully understand why I bought the 8x42 Trinovid when I already had the 7x42 UVHD+ I'd have to bore you with the whole story of how I came to buy them, but suffice to say that I paid only a third of what a new 7x42 costs (they were an ex-dem item). However, the fact is that 8x is 8x, and not 7x(!), and whilst I'd happily give up a little detail retrieval for the benefits of the 7x42 it's nice to have an 8x format bin as well. In addition I like the ergonomics of the Trinovid. I have no problem with the extra weight and the armouring feels slightly nicer to me. The UV's armour has a slightly 'sticky' feel which offers more grip, but I just like the feel of the Triny a bit more. I also slightly prefer the focusing mechanism which, because it has a stainless steel mechanism instead of titanium, feels a bit smoother. At the end of the day the view from the 7x42 is better in every way, but the 8x42 Trinovid still has that lovely Leica view, comparable by all accounts to the original UV, and I simply couldn't pass up the opportunity to own the best iteration of the Trinovid in a format (8x) that I wouldn't otherwise have.
I can really relate regarding the Trinovid now, I actually like it even more now....
So I've had the 7x42 HD+ for a few days now.
Here's some initial thoughts compared to the 8x42 Trinovid (second most recent, centre diopter).
It's a bit brighter, has less CA but still can be seen, is noticeably wider in FOV and a bit more DOF. Regarding the Trinovid it has a much smoother focusing wheel, feels better in my hands and handles better, while being a touch less bright I can actually see more detail with it even in shadows or low light due to the higher mag (did some flying fox watching in low light late evening).
So what's to gain... well nothing really, on that note I can see why they dropped this particular Trinovid so soon as it's excellent and must be extremely similar to the 8x42 UV. I had intended to sell my Trinovid in as new condition but I can't do it and actually like it even more after the 7x42HD+ comparison.
In summary, 7x42HD+ gives a bit of extra FOV, DOF and less CA, mildly brighter.
8x42 Trinovid feels much better in my hands, focuses much more smoothly and feels more precise accordingly, shows more detail with the extra mag (quite noticeable between the 7 and 8x, this is also a bit of a toss up as it's basically a matter of a bit brighter and a bit more steady vs closer view with the higher mag), can show CA more readily but likely only when searching for it particularly in difficult lighting.
They are both good but surprisingly I can't say the 7x42HD+ is better, just different. Without comparing I'd hazard a guess that the 8x42HD+ would be very similar to the Trinovid if not identical to the HD or BR.
I'll go as far, at this point which may change in time, that I'd even favour the 8x42 Trinovid over the 7x42HD+ but they are different enough to hang on to both.