The desktop app should have maximum encoding compatibility so you direct play. It's not guaranteed with browsers e.g. I believe Firefox doesn't and will never support HEVC.
My gripe with the desktop app is lack of ability to easily refresh like with a browser. The UI bugs out sometimes and I end up having to close and reopen the app.
I like the new EVA, but I don't like the idea of completely dropping the old. As the main movement pose it just doesn't make sense ergonomically, needing your face turned basically 90deg from its natural position. It also makes you look like you're moving through any regular old fluid instead of space. I would hope they add a toggle using something like the prone key