The Kaiser System V is a modular system so all parts are interchangeable and can be upgraded by swapping heads, condensors, columns and boards. Masks are common to all.
They also made a basic enlarger which didn't offer this functionality.
Naming conventions are;
VP35XX upto 135 format
6XXX 135 or 120 upto 6x6
7XXX 135 of 120 upto 6x7 (no longer produced but still compatible with 6XXX and 9XXX series)
9XXX 135 or 120 upto 6x9
AFAIK the last digit denotes series e.g. latest are XXX5
Three heads were made, Colour, B&W opal with filters and a Multigrade head. The latter in no longer made.
The System V are well made, fairly heavy and more than adequate for amateur use certainly. They still sell for reasonable money used. (About 20% of new cost but this varies due to the last point below)
The enlargers and most parts are still available new. To some that is an advantage over discontinued brands, although (generally) an enlarger is a fairly simple piece of kit.
Choice of photographic enlarger is often a personal thing, and people may argue you need X Y or Z brand, but most will do the job within their format limitations.
Equally important is what brands are common in your area, so are easy to obtain (new or used) particularly as used they don't mail particularly well....Hence often you can get them cheap if you are willing to travel or are lucky!