I use my CND lamp with my ACG and have zero problems whatsover despite what the manufacturers state. In fact all my prep products that I use are CND's too. Gelish are hardly going to recommend another companies products.
I use 2 systems and find I'm also able to offer something to everyone.
Shellac isn't a cure all for every client, just like ACG or any other gel polish is either, nothing wrong with a bit of variety.
I love that someone actually get that!! CND Shellac or gel polish isn't for every client!!! It's soo hard getting that across to clients and nail pros!!