I write applications to run on the quest and it's miserable. Simply getting your apk onto the device is the most unnecessarily difficult things I've ever seen. In order to unlock developer mode, you have to have a Facebook account with your phone number associate with a Facebook developer group for your company which requires additional verification to set up.
Then you are required to install the oculus app on your phone and link it into your Facebook account. If you're lucky, this will work the second or third time you try it. Even then, sideloaded apps are hidden away in a separate menu.
Oh, and you think you can just use your quest tethered while you work in Unity? Good fucking luck. It's remarkably unreliable and unstable. Usually I get a black screen until I restart my headset, my computer, SteamVR, unity or a combination thereof. It's been over a year and I still don't know what the right incantation is. If you want to try air-link, you don't get hand tracking. Intentionally. It's not a technical limitation.
Beyond that, it's mostly-standard Android, which is also painful to develop for, but in new and exciting ways.
Conversely, targeting Valve Index and an ultraleap tracker is as easy as it gets. If your application runs on the PC where you're developing it, you're already done. It's plug and play almost every time. There's no extra layers of bullshit to wade through, you just open unity and hit play and that's it.
Well, unless you count all the ways that PC development sucks.
Development concerns aside, the quest is a low power phone with some cheap optics. Resolution is bad, frame rate is bad, battery is bad, it literally does not fit my face. I can't see anything because you only have three IPD choices and they're all wrong. Hand tracking is consistently worse than ultraleap, and with the latest update it's totally unusable for me. And I mean that I literally cannot select UI items. It nags me every 30 seconds about turning on my controllers. I also have this weird issue where different colors render at different depths. Red text floats above the surface and green is sunk below. It's really hideous.
The Quest is worse than a PC HMD in every way except that it's cheap. That's it, that's all it has going for it. It's cheap and technically does run VR.