I enjoy choosing my own, so no direct experience. Having known people who have joined these clubs, however, I've be especially leery of those clubs that offer "rare" ,"boutique" , "very hard to find" wines for reasonable prices. What it looks like you usually get is some relabeled plonk no one else wants. What I'd do instead is one of the following:
1) Some reputable wineries have their own WOTM clubs. If you find a winery you (or rather they) like, see if you can do that.
2) While I've never joined, some reputable retailers also have their own WOTM clubs (I know I've seen at klwines.com). I would think that they would (a) be choosing fromtheir regular stock and (b) hoping to add to their regular customer base.
3) While I understand it's kind of cool to get a package with a new wine every month, a LOT of your money goes for shipping (a typical retailer shipping from CA to NY ground will charge $25-40 a case, while a single bottle is probably $10). You might consider getting your parent a one time gift of 6 to 12 bottles from a good retailer. Chambers Street Wines in NYC is well-known for putting together interesting assortments, and most other good retailers would do the same. If they mainly like reds,you could do one left-bank Bdx, one right-bank, one Cal Cab, one Cal Merlot, one Shiraz, one Ca Syrah, one N. Rhone, one S. Rhone, one Tuscan, one Piedmont Nebbiolo, etc. If they prefer whites, then....
Good luck with whatever you decide!