PLOC is an amazing way to build your credit, but not in the way you expect. They are great because they can help guarantee you NEVER miss a payment.
Use the PLOC or an account linked to it to set up an automatic monthly payment to the credit cards that you actually use, ideally paying the entire amount if your bank offers that service, or else a regular payment that is guaranteed to be above the minimum and ideally close to your ordinary spend. Then you make a second manual payment to top off the difference. Also have your utility bills, rent, car loan, mortgage, etc., all paid from the same PLOC or PLOC linked account.
Then set up your employer to direct deposit into the PLOC itself.
Now what happens is that you are guaranteed to be paying the PLOC in full every month because your salary hits it, then your credit card and other bills all pull out using the PLOC as necessary. If your salary goes in a few days late? Or you overspent a little? No worry, the PLOC has you covered.
I have a PLOC that has a fairly unfavourable rate of interest (like 10% or something) but I don't care about that, it either never has a balance owing, or if it does, only for a day or two until my salary hits it, so the 1-2 days of interest is pretty insignificant.
You will want to experiment with this before you set it up fully, I gather that not every bank will be OK with your PLOC having a large positive balance, which it will most of the time when your salary hits it. Obviously you get NO interest when you have a positive balance -- but it's just meant to be a clearing account when used this way. Any actual savings should move out of the PLOC into a real savings or investment account.
I think they are fantastic when used this way. I say they help your credit becuase once this system is running you are pretty much guaranteed never to have a missed payment, even if you got hit by a bus and you were hospitalized for two months -- the whole thing would tick along automatically turning you in the long run into a credit score rockstar. Provided you are actually spending responsibly it pretty much eliminates negative information because you just forgot what day it was, etc.
