Just completed 1k games at the Spades app by Karman games. I thought it was worthy of remembrance.
The AI plays terrible of course. I have seen it overtake Js of a nil-bidder and return a spade. Most of the games the bid ends in 10 trick total and you are usually able to donate most bags to the opponents.
I think winning 70% is nothing to sniff at. Give it a try. More often than you'd like, your opponents land a couple of NILs or your esteemed partner fails at one and the comeback is hard.
I never use UNDO for correcting mistakes btw. If I miscount, I take the loss. I only use it if I make a mechanical error (misclick) and sometimes when I failed to see a NIL bid (oh he did NIL, lets not lead this Kc then).
The stats are interesting. I do less NILs (variance is bad for you), I fail more bids, I bid higher, I make less tricks and I win predominantly by getting less bags than the opponents.
The "Bids saved by partner" is amusing and ought to be renamed to "Bids I saved my partner from oodles of bags"