Why 3X21?? Go with the 3X24 Makita 9924DB, it can also run a 4" belt when
needed, low cost (the Volvo of belt sanders) great value for money, they
have been making it virtually unchanged for years.

I second this choice. I bought one based on the advice of a cabinet shop
owner who has half a dozen of them that have seen daily use for the last 7
years, with zero problems. Dust collection on the Makita is pretty good for
a belt sander, and it's not as noisy as some other brands.