Ha! That's the R 195 L. L meaning Laser - the base was specifically designed to fit on top of the hiking strap/centreboard brake fittings like that. It's still made by RWO, renamed R 1955:
RWO (Marine Equipment) Ltd
This was never a widely popular choice even in the 1970s, but for decades, it was the only legal alternative to the side deck cleats (or no cleats). I think some successful Master used it as late as the 2000s (Mark Bethwaite, I believe - Aussies, is this correct?), and the charter boat providers at regattas weren't exactly happy when he drilled holes in their hulls!
But at some time during the last 15 years, this piece of equipment was deleted from the class rules. The current rule allows a block with any kind of integrated cleat, but it has to be attached to the eyestrap on top of the hiking strap plate. So yes, that fitting is illegal! No grandfathering.
As for functionality, the only good thing is of course keeping the ability to cleat the sheet while having clean side decks. The lack of a ratchet is bad, and you probably can't turn the cleat arm (horizontally) much without getting a very unfair lead. Also, the vertical cleating angle has to be a compromise that works in some conditions and on some points of sail, but less so in others.