In all honesty, I used to use it when I first started almost 15 years ago, but haven't used it since my training with CND. To be honest, I (like most techs I know of that use it) mainly used it as a prep substitute as it is 100% methacrylic acid (cleanse by fire!). Depending on your system, your prep should be sufficient enough for cleaning. Acid primers should only be used sparingly to promote adhesion when the product cant obtain at least a hydrogen bond by itself.
Just because a product can benefit from a primer (acidic or not) doesnt make it a bad product. Ultimatley what defines a great product is one which gives you the results you aim for in the salon in the safest possible way.
Thanks for the reminder about that article Fiona... brought back memories