For me the answer is pretty obvious: for sure you should use it.
A few things why I think so:
- the learning curve is very straightforward and not so difficult
- pnpjs is a wrapper on REST API, by using jQuery\REST you will create your own "pnpjs". In that case, why reinvent the wheel?
- pnpjs has some other things except just wrapping around REST. For example caching, batching, managed metadata support (which is not supported in REST yet)
- fluent interface is awesome in pnpjs. I believe you have less typo errors and regression bugs with pnpjs
- your code is cleaner, as a result easier to maintain