With my basic mani pedi cert, all the major distributors allowed me to buy products.
However, no insurance company would cover me for sog without any knowledge in a system. The proof that you have that knowledge is your certificate.
Now "technically" insurance isn't a legal requirement, as far as I am aware. If you have millions in the bank, you are able to cover a court case yourself. Insurance is there to product us, in case anything ever goes wrong. As with all insurance types, you won't be covered without showing a level of care to prevent a case from occurring in the first place. Car insurance, you need to have a driving license, home insurance you aren't covered if you don't lock your front door, etc.
Different insurance companies have different requirements. When IBX came out, many people were saying their insurance refused to cover it. IBX created a class for this reason. Training originally was not needed to use the product, but it was a requirement from some insurance companies.
Even if you only pick up a couple of tips from a class, you will always gain something. You also gain the support of an educator and a lovely new certificate. Training doesn't have to be expensive, infact a few brands offer it for free if you buy a starter kit.
I am an extensive researcher. I looked into so many brands, fully read multiple 60 plus page threads on salon geek and watched hundreds of YouTube videos. Even though by the time I came to do my training I didn't really learn a lot more than I already knew, I did have someone standing over me and confirming I was doing the right thing and I did pick up tips. I point blank refused to buy into any brand until I had some training booked. I only did my sog training this week (!) and I won't be advertising the service for another month, until I have done a wear and removal test on myself and feel confident in my service. I don't want to be ironing out kinks and practising on clients.
Sorry this is insanely long, but it's important to clarify the distinction between what you can do and what an insurance company requires you to do. They are all different, so you must ring your own provider and find out. Some will allow one certificate to cover you for multiple systems, others will require a class in each system. All it takes is a quick call to ask and we all know how insurance companies love to find loop holes to avoid paying out. It's always best to double check. It might mention gel on your policy, but you may find you aren't covered without a certificate, or maybe you are! Ring them! But a course and certificate will always hold some value.
Good luck with whatever you chose to do! Xx