I'd do some research. In my area, and for my (prospective) clients, most of them have heard of Shellac but don't know what it actually is whereas I know some people who will specifically ask for Shellac. This could be a major influencer in your decision if you're in an area where people specifically want Shellac! I've had Shellac on myself a number of times and once I could, I bought a few of the INK colours. I love the INK, but definitely want the training, I just can't afford it yet. Why not buy the rock top coat and a colour from INK and see how you think it compares? There are enough pro tech Facebook groups I'm sure you could sell them on if you decided you didn't like it. No point investing in a system if you don't see the benefits of it as a tech x