The sound of the Alesis Monitor One MK1's is overall pretty good. While certainly not the most accurate monitors in the world in terms of having the full frequency spectrum covered, they do seem to be pretty true and translate well. I'd compare them to something like a Yamaha NS-10, but I think they sound a bit better since they cover the low end a little better. They're probably not the best for mixing, but can do the job if you know them well. I'd recommend them for a home studio owner or as a B set of speakers in a larger professional studio.
The Alesis Monitor One MK1's aren't a bad choice for a budget set of monitors for your studio. They're not going to change the game by any stretch, but they're solid and shouldn't cost much if you can find them used. If you can't, there is the MKII version that don't cost a lot, although I don't know exactly how they compare here. Overall, these are a cool little set of monitors but probably not for the pro's.