Kei marine was built by paddy Hart in east london. he is still around, But unfortunately when he and richard Carrol (his business Partner) split, the moulds also got split between them and somewhere along the line the moulds got burnt.
As far as modles go, he built the 24 Scorpion, 24 Kei mono. As far as I have heard, different boats. You get some without chines (not sure why). I also seem to think there was a cut down 21ft version of the mono's
As far as cats go, he did a 18ft kei cat, Very solid. You got a semi cabin and a fwd consol of this. Then in later years he built a 15/16ft Wild cat. This was done in centre, wfd, cabin (for LTB) and then for rubber ducks. I have this boat test in a ski boat mag at home.
Paddy is still in the game, but mainly in the refurb market. He is based here in el. i have his nr if you want to talk to him. Sure he can give you back ground to all the boats.
I have been on almost all the models. Very strong. safe boats. the 24's I go on both run 115 2 strokes. plenty power, but quite thirsty. The one perviously ran an inboard, and as a result has lead balast built in up front. makes the ride in following sea a bit hairy unless all crew are far aft. It alos has no chines and as a result the tail is very loose. The other one rides very nicely.
Sorry forgot about the one catch 22 ghas, Dont know that particular boat, but sure paddy can help you out.
I am sure in old ski scene there would have been boat tests. Just by the nr of them still around, in EL, PE, CT you can assume they are good boats. Not too many new monos in the size range of the kei 24's so they will continue to be popular with guys that like monos.