It's a very decent sounding piece, with 4 perfectly usable preamps....
OTOH, for not too much more, you get an Aardvark Q10 which doesn't have adat, but has 4 more mic inputs, another pair of outs, better preamps (my opinion), and some usable (not great, but certainly has its moments) effects processing on board. The Aardvark 2496 is a bit cheaper than the Echo, but has roughly the same features as the Mona, minus one pair of analog outs, word clock, and adat, but keeps the effects processing section.
The fact that the Mona is discontinued doesn't bother me too much, because it uses the same driver model as the other products from Echo which are not discontinued. If your friend is looking at using the Mona via Cardbus, his next step up would be the RME stuff, which is very good, but pricey. If he needs ADAT support along with other stuff, then the Mona's a decent bet, but if ADAT is the primary thing, why not go for the much cheaper Gina as a solution? If he's just looking among PCI card interfaces with mic preamps, there are other interfaces (like the Aardvark and Egosys) which provide better value. If he's used Echo stuff in the past and it's worked on his system without problem, the extra hundreds of dollars for peace of mind on installation and setup might very well be worth it.