My feeling is that it’s too complicated and most people won’t understand (and therefore won’t fully appreciate) how generous this loyalty discount is, You are offering the equivalent of a 5% discount off the cost of your manicures if clients have 5 manicures and if they have 10 manicures this becomes a whopping 12.5% off their previous visits
Why don’t you just work out how much it is in money and offer a loyalty card needing 5 visits that earns them say £10 off a spend over £40.
I’m not clear why you want to discount your prices to the clients that love you the most. I get that you want to reward their loyalty but offering a free manicure on the tenth visit just makes me feel that you’ forced your clients to overpay on their previous visits in order to fund the free manicure. I also feel in principle that you never want to give away your time because your time is not a scoop of coffee and some hot water, it’s a very precious commodity and you value every minute.
Why don’t you offer something that costs you less? Like a free solar oil, or a free nail repair.or luxury upgrade? If you offer something that the client can “bank” and treat themselves to in the future it becomes special. If some of your clients don’t have nail art you could offer a single nail of art - say a flower or something where you can show off your artistry. I just think that having a free French polish upgrade or free chrome might feel more special to the client than a free gel polish underneath nail art.
I think that beauty rewards should encourage clients to try something new that they wouldn’t book and pay for normally. That way it becomes a marketing tool that may lead to future extra business.