Haven’t used it and wouldn’t advise it for a kart having read their site. “Real” race gas is about consistency of batches and performance additives. Octane numbers for race gas vary depending on the application its intended for. A higher octane number doesnt make it a race fuel. VP have many 87MON racing fuels for example.
Bottom line is that, at least with a carb’d engine and especially with a stroke putting out semi-decent HP, I’d very hesitant to use that stuff because you are blending it with pump gas which is a mixed bag in terms of composition and specific gravity. What works one day may not work the next.
If you have EFI with O2 sensors and so on, you can get away with that, but I would still say it’s sub optimal.
Last thing to consider is the presence of lead, which while not healthy for your or me, is great for the internals of a two stroke.