Questions about binding keys to the keyboard and the Synapse software

I’m thinking of buying the Huntsman TE keyboard but there is a problem. The keyboard only comes with international key layout and it doesn’t have some letters used in my country. I want to bind the keys that are not included on the keyboard, to the keyboard and switch between the real keys and the binded keys(possibly with hypershift? https://xender.vip/). So when I press the keys normally they would register the keys that I added in and when I press the keys while holding the FN key they would register the keys that actually exist on the keyboard. I tried to explain as good as I can. Also does the Synapse app have a lot of issues as some users state that it is very bad? Thanks.