Just tried one of these on an XL Fluxo. As Chris has already pointed out the fit is awful particularly on the mouthpiece but the rubber seal is too narrow for the ceramic cup and too small for the tube bore.
So I fitted the seal and tried to use it with a drip tip. It vapes quite well but without the mouthpiece seal juice can migrate past the cup seal through the filling slots if you lay it down.
The wick slots seem way to narrow to me and nowhere near deep enough, and the whistle tip is just going to be a juice trap and cause long slow draws to be needed. Also with a flat tip we go back to having to align the clearo again unless you are one of those peculiar types that prefer mods with switches on the bottom end

- a round tip like a cannon drip tip does away with this faffing about.
I think if the cup seal was made to fit the cup and the tube properly, and the tip was redesigned like a short cannon drip tip we would have something far more useful.
Not knocking the GotVapes guys, kudos to them for trying new things. This is my attempt at honest feedback to help improve the products. Chris, Danno - so many clearo lovers swear by the drip tip... we really do not need to go back to whistle tips... the cup seal design is great it's just the fit on this batch that is lousy, but please ditch the whistle tip and redesign the kit with a drip type tip. Then you would have a real winner IMHO.