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Well you can always get a cheap GSO varient. but they are just that Cheap... if your planning to do astrophotography then you need a decent focuser.
As for slimline, you start looking at FLI PDF or Atlas focusers other wise you are looking at about 100mm for most 3" focusers and 3.5" even more.
At the end of the day its about what you want to do and how much you have to do it with and the last point how patient you are. I waited 3 years to upgrade my focuser... it was tough because i knew it wasn't good! but i did the jump in one foul swoop standard SW to FT.
I look at it in this light, if a 4 way adjustment was the best way then serveyers would use 4 legged tripods. The do not. you need left right back and forward if you use 3 adjustments it pivots off one pivot point, if you have 4 you may need to adjust 3 different points to make it sit properly or else it there will be different pressures on each of the 4 supports.
As for adjusting in X,Y,Z your only wanting to adjust in X (towards or away from the focuser) and Y (side to side) plane, Z is taken into consideration with the central bolt to bring the whole secondary hub and mirror up or down the tube.
Come to think of it everything pretty well uses 3 adjustments. Mirrors, secondarys, laser collimators etc. etc. why re invent the wheel?
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