I owned an SU1 for a while. As a vertical miller I found it an effective machine, accurate and fairly sturdy, albeit, as said, with limited height under the spindle. The mounting of the spindle on the sliding overarm could be useful for some set-ups to gain extra throat depth.
As a horizontal miller I was less impressed. The minimum speed was rather high at ~200rpm, at which point torque was low and rotational speed was becoming uneven. I found that steel could be usefully cut only with fairly small slitting saws, although, obviously, more was possible with non-ferrous metals.
A point to note is that the spindle and motor assembly is fairly hefty and needs to be slid into a close-fitting bore for the horizontal set-up. To do this, I needed to be able stand at the rear of the machine, so positioning it close against a wall would make for very awkward handling.