Agree with both of these. I like to have a little ditchable weight, and the waist pockets allow for that, as well as for trimming out nicely. You can get a well made and inexpensive AL plate here:
Backplates and Accessories
I have 2 of the aluminum and 1 of their steel, and have been using them for about 13 years. No need to pay outrageous prices for them. You can take these suggestions as a starting point, but ultimately you will have to experiment a little and find out what works for you with regard to proper weighting for NB and trim. With a steel plate I use 2 1# in the upper tank band pockets snugged right up to the plate, and 2 1# weights in the waist pockets. With the AL I use 2 3# weights on the tank band, and 2 1# on the waist. This is with a full 3mm wetsuit and aluminum tank.