Would you use a Third-party SaaS boilerplate to bootstrap SaaS startups?

As a techie, I can write all the boilerplate code for standard stuff like auth, billing, payments, email distribution etc etc. OR I can buy/use off-the-shelf startup boilerplate source code.

Both choices have their pros and cons. First choice gives me higher confidence, customization and know-how but it could be very time consuming.

While the latter choice may save me a lot of time, but i don't feel comfortable taking someone GitHub repo and using it as base for my SaaS. My main worry is that it may take me even longer in the long term to understand that code and maintain/extend it.

How have you tackled the above situation ?