Haven't used date check.  P411 is about 50/50.  Providers seem a little wary of P411 IMHO.  You can use it, but you need back-up of some sorts whether reviews on a site or a couple of other providers to verify.

I guess if you were LEO you could set-up a fake account, have other LEO with accounts as providers vouch for you giving you the appearance of being a legit monger.

One provider kept asking me questions about me and the hobby - even after we finished the 'act'.  

Weird

I've met a lot of fine ladies through Date Check and it's a great reference source. When the lady is a DC member the verification seems to go faster.
I've never used P411 just because I found DC first and it's worked so well I haven't needed any other verification service.

While I have used both successfully in DMV and on the road Date-Check has to many providers who are no longer active.

P411
More up to date w ladies. Easier to see who is avail and when
Can see last time they logged in ...helps to know if they are active
Private message works great
Can block providers you have no interest in seeing creating a better bucket list
Cleaner site with minimal ad clutter
BUT....costs $129 year. It has saved me more than that in p411 discounts from lady  

DC
Lot of dead wood. Ladies you never hear of and aren't reviewed. Of course there are active providers too
..just more clutter.
No messaging
Crappy ad board
Can't block providers you are nt going to see
Functionally have more clicks to see pixs and ter reviews
BUT. Only cost like $89 for lifetime subscription. Don't recall seeing anyone that offers a dc discount. Probably more unlikely.

And use other tools for research, such as the many review sites as well. Need all the tools for research.

BTW, for the ladies, P411 only offers an OK if they have seen them. Have heard that D-C does have somewhat of a rating system for the clients - Highly recommended, recommended, and not sure what the others are. So, its good to be on both.