It is a very good amp. One thing to note about old Marshalls, however, especially on JCM800s:
The pcb on an 800 is not the best, and the way they are mounted, they start to warp over time. Plus, the power capacitors start drying up after about 15 years.
If the amp is local, I would have it checked by a qualified tech before buying.
My 800 needed to have the board and power supply caps replaced due to its age.
Sonically, it is as good as the 2203, and I sold mine for a fair amount of coin.