You should actually read the mod page and realise that it doesn't require any payments at all to function. The modder simply gives out custom models to those who donate to them. This is very warranted and not unheard of in the modding community, especially to those with a Patreon / Ko-fi etc.

Modding is often long and tedious work. Work done for free, so you can have an enjoyable altered experience of your game. Many people like to show their appreciation and support to modders for their hard work through donations. The fact that this modder is giving out exclusive content to those who donate to them is extremely generous. Nobody is forcing you to donate, and there are many modders who don't give out anything for donating.