The Index is very old at this point and starting to show its age. It's still functional, but there's much better headsets out these days. The one good thing about it that a lot of modern headsets don't do is lighthouse tracking. Essentially, little IR tracking cameras you place around your play space mounted to walls/tripods that super accurately track you in 3D space. Very precise and tracks from all angles. No batteries but requires a wire to your pc to run which can get in the way.

The Frame is a their more modern headset. Still not bleeding edge specs, but still lighter, smaller, and better functionally in a lot of ways. But it's inside out tracking, meaning the cameras are on the headset itself. Good for tracking your hands/controllers right in front of you, but middling at tracking at waist level, and unable to track behind your head. This is the standard a lot of the industry is moving towards. Functional for 90% of games and all-in-one so no mounting, but definitely a less accurate technology. Wireless by design so no wire to get in the way, but limited play time because of the battery on-device to facilitate this.

If you're trying to decide between the 2, get the Frame. It's more likely to be supported for much longer since it's new and the Index seems to be getting phased out now.