Student OTJ Training Question

Hello to all,
I've been lurking in the shadows for a couple of months, reading and trying to learn all I can from the posts. And I must say "thank you" to everyone that has contributed to this forum. It's filled with a wealth of information and solid advice for those of us new to the industry.

There are a few of the mega carriers that will bring someone in, they get their permit and then spend a few weeks out with a trainer before testing for their CDL. Now from what I've been reading, I get the impression that some of the trainers ( Not trying to generalize that all trainers do this ) take advantage of having someone else run miles under their log book while they "rest".

So my question is, are their trainers who really do this? If so, is this the norm? I understand that once a student has gotten his cdl that a trainer wouldn't need to be holding his hand while completing his training, but anyone who just has a permit, in my opinion, needs the extra set of eyes and experienced guidance that their trainer is getting paid for.

I'm in the decision process right now of which way will be best for me to go with for my CDL training. Either a place such as Prime or one of the local "mills" and would appreciate thoughts or comments from the people who "have been there done that".
Thanks in advance