I had a 4x24 Craftsman for about 25 years and when the bearings packed it in I bought the Porter Cable 4x24 'cuz I had quite a collection of sanding belts. It's quite heavy, which is good when leveling plywood seams of a floor or flattening a large surface, like a bench top, but makes it a monster for edge sanding, such as scribing a counter top to an uneven wall.
formatting link
more portability I bought a 3x21 Ryobi "in-line" sander and it's great for scribing and general use in a non-flat position. It's very similar to the Bosch sander you referred to. Being a Bosch fan I doubt that the Ryobi is built as well as the Bosch but I found many great reviews for the Ryobi before I bought it and it was less expensive than the Bosch. The "side saddle" drive mechanism of the PC, Makita, Dewalt and others of this ilk prevent sanding up to a wall with both sides of the machine... and sometimes it's impractical to turn it around. The "in-line" style of sanders works well in that application. But the 'in-lines" tend to be lighter and less powerful. The Ryobi has performed very well so far and I'd recommend it (or the Porter Cables, too).
formatting link
acquiring a collection of 3x21 belts, I had the chance to score the
3x21 Porter Cable (baby brother to the 4x24) for a ridiculously low price, so I grabbed it. It performs every bit as well as the bigger one but, as I said, it's a bit heavier than the "in-line" design.
formatting link
've never been concerned with dust collection 'cuz I seldom use a belt sander in a pristine environment. I'd say that the dust bags on the PC models and the Ryobi are about 50% efficient and I think a shop vac would kick that up to 95%.
In my humble opinion, variable speed is a must on this type of tool.
Hope this helps...
Cheers