I always tell people it's decent but nothing special. Other compounds are "better" in many ways and they are cheaper and dosed higher per ml so require less injections so are easier to run. It has it's place and people should try it but if you're a newbie and wanting to grow don't be buying 2 vials of primo thinking 2000mg over 10 weeks (using 100mg/ml for my example) is going to do much. You would be so much better taking 2ml deca or eq (600mg) or even 2ml mast e (400mg). Now for experienced guys primo with test can be very useful and for many it means no AI is needed so if you dose them correctly (best ratio for you) they can be a very effective and a "safer" combo than most other things.
There will always be exceptions to every rule so it's worth experimenting with it and seeing how you personally respond. I know quite a few big people who love primo and dose it most of the year. Primo didn't do loads to me and I high dosed it to see exactly what the compound would do at over 1 gram. Now it does compliment a physique very nicely and simply makes you look better so it has it's place but for me it's stuck in the middle in a sense. By that I mean it compliment's things nicely but I prefer other compounds (get more out of them) when I have exact goals. For growing I prefer test, deca, adrol etc and for cutting I prefer test, tren, mast, avar, winny etc. Primo at 400-600mg can assist any cycle and it will give you results but for me I like it as an add on when growing. The other time I would consider using it is for maintaining over a longer period but wanting to stay extra sharp (so an enhanced cruise).