There are many, many more providers reviewed in TER than will ever appear in P411. If you seek maximum variety, mixed with a bit of danger, then the numerous backpage advertisers with one or two reviews in TER are your ticket. Occasionally one of them will pop up in P411 but it's pretty rare. If you just like to sample from the large and fluid group of ladies who dabble, stick with TER. That's not to say that well established providers don't use backpage also, and all of them are reviewed in TER, but they can get lost in the throng.
You absolutely can search providers in P411, but it does not offer reviews or scoring. It's not in direct competition with TER which is why TER allows us to mention and discuss P411. If you like to have a very clear idea what to expect before your first visit, the best way to get it is to read 8 or 10 TER reviews of the same woman, including both high and low scores, and average them out in your mind. I've never been surprised after going through that process.
Services on offer is another issue. P411 offers a section where the ladies can enumerate services, but it isn't required and many don't use it. So if you want to know which of the acronyms will likely apply, VIP access to her TER profile is your best bet.
P411, on the other hand, offers ease of access, in the sense that it's much easier to book after you get a few Provider Okays in place; a sense of security, because a provider can't get into P411 unless she either has an established track record of reviews, or else receives an invitation from a gent who is himself established in P411; and overall, considerable assurance that the lady you see will be a quality experience at a rate as good as, and often better than, you will find anywhere else. It also gives you the option to fill out a profile of your own - tell her a little about yourself - which might make her more comfortable when the door opens.
Then there's travelling ladies. Several agencies advertise on TER that you won't see in P411. Same with many independents. But it's also pretty common to see ads in P411 that never appear on TER. And there's an agency that reps porn stars that is advertising in P411. I haven't tried them, but if they accept P411 Okays it is probably your easiest route to an expensive but possibly very fun experience.
If you travel and want to hobby while you do, P411 is awesome. Get it. Use it.
Overall, the group of Minnesota women in P411 is somewhat static. One will disappear, two new ones will appear. Nothing like the turnover that you'll find in TER reviews. So if you want the thrill of that first glimpse of a new lady every time the door opens, probably stick with TER. If you prefer the pleasures of an established relationship with 2 or 3 quality ladies, or 10 or 12 for that matter, P411 can serve you very well.
These comments are all IMHO. But Bridget's point about a free six months of P411 if two women will vouch for you seems like the clincher. That wasn't available when I joined. You'll probably still have to give them some personal info to sign up and for some that is a deal breaker. But their servers are in Canada, where prostitution is not illegal, and they have promised loudly and repeatedly that they will discard all personal info once you are on board. So make your own choice in that respect, but six months free sounds awfully good to me.