>>289356334
The main advantage of going all in on an Index to begin with is the clearer path to full body - Will you be spending a lot of time in vrc? There are many drawbacks beyond the price too, namely the bad reliability as the other anon said. I would personally say get a Rift S, but if you have the money [spoiler]and are willing to buy a spare set of controllers[/spoiler] the Index is reasonable.
>>289356757
The cosmos is shit, the Rift S is far better for the price. It does offer a better upgrade path for full body, but imo it's not worth it. The extra cost of the cosmos could also go towards getting basestations for Rift S too.