My main use (not day in day out) would be for box making (mainly) and for clamping edge jointed boards together (from time to time). The slight hesitation is that 300mm would do most of the box making, and 600mm would do almost all of everything but is the extra length going to be a nuisance on most box making tasks. If bessey or anybody else reputable did a 450mm available in the UK, that would be ideal.
I also have some of the pipe clamps but no pipe yet. That could persuade me towards the 300mm k bodys
I also have some of the pipe clamps but no pipe yet. That could persuade me towards the 300mm k bodys