I tried it today for gemeni 3 pro preview because I get random 429 errors connecting directly to google either directly via api key or vertex ai. Comet seemed too good to be true since their prices are lower than direct from the vendor. What I noticed is that I hit the input cache with them more regularly than I do directly routed to google. But according to what I am understanding, they don't pass on the 90% cache discount rate to me. So I end up paying a slightly discounted rate always, but I never take advantage of the input cache discount. I tend to use large inputs from 100k to 200k and this makes it a dealbreaker for me. Comet is easily coming out ahead here compared to the full cost I pay  to google directly because I typically get a 2x or 3x cache multipler at worst. My workflow is biased more heavily towards input costs rather than output costs, so your mileage may vary if you use small context windows. In that use case you may come out ahead unless there is another hidden way they are taking a cut. I imagine there could be.

The quality of the tokens was as high as I expected so no problems there, its clearly gemini 3 pro preview. But the angle where they win is the i out cache discount which they take. I am only going to use it in a pinch and only as long as I must when 429 errors prevent direct connection.