Based on what I see, this is a 22 lr that was probably used in Bullseye Competition. The grips are undoubtedly something the owner fashioned for himself. You see highly customized pistols all the time on the firing line at competitions.
There is a lot of finish missing. Before any serious consideration of purchasing I would push a patch and a bristle brush down the barrel to see if the barrel has rust pits. Based on the exterior, the interior might not be so great. If the inside of the barrel is perfect, it is probably a good barrel. Competitors replace factory barrels with match tubes, it does not make sense to spend all that money to put on an inferior barrel.
But, I am going to say the price of $488 is overpriced. Customized pistols are worth less than factory original. As a general rule, people don't want them because they are an unknown. Look at the price of an excellent condition MKII and if they are close, go for the MKII or talk the shop way down on its price. I just looked at Gunbroker and like new MKII's are going for less than the asking price of this pistol. I think the MKII is the best of the series, don't have a MkIV, it may be better, don't know. Stay away from MKIII's. The chamber indicator is a source of malfunctions and the magazine safety makes assembling the pistol a confusing puzzle.