When I have used grid switches I have always used MK because they have a wide range of products and seem reliable. But they are expensive. Are any other manufacturers’ products interchangeable/compatible with the MK ones and if so what is their quality like?
The MK use a plate to put switches in then a cover over that plate, in the main all steel and screwed together and needs a deep box, in contrast the LAP use a plastic clip in system there is a final cover which clips over the plate to hide screws, but once assembled it is more like the non grid systems. As you say each system has a different range which will fit in, I have used the LAP with a single socket, fuse holder and switch (4 module) to replace a double socket to take multi sockets from a spur. Also they have brushes, which allows one to make multi TV and satellite leads coming into the house look neat. Each system has + and -. Not seen the multi named switches with LAP that you get with MK so for kitchen use MK likely still king.
You should take a look at Click Scholmore, Just about all the ranges are customizable including the metal Deco ranges with different switches and modules, The Grid pro range will fit an MK yolk but im not 100% certain if they fit the MK faceplate as when we did it we had to change the faceplate from metal to plastic anyway so didn't need to check that. There https://scolmore.com/products/gridpro/
Agree click scolmore prob best on the market at the minute, mk overpriced and not the quality it was once