Because they do generally refund you the cost of return preparation and the RAL costs, I have to assume these are legitimate shops. But here are my standard questions:
1) Is it worth a hit to your credit to qualify for a RAL? My understanding is that perhaps some of the shops this year are not actual loans so do not require a credit check, but I would sure check the shop carefully before I allowed that hit.
2) In order to make sure that at the last minute your shop is not acceptable because you aren't entitled to a large enough refund, you really do need to do your taxes before you take your taxes to be done. So why are you doing the shop?
3) In order to complete the shop you are going to need to have the preparer actually file your return while you are there. This does not give you an option to look over the return at your leisure before filing, so any changes or corrections will need to be filed as amendments.
4) The big question, however, is why are you providing interest free use of your money for as much as a year to Uncle Sam?