In my experience it is a risk/reward issue. Not that there is much risk.

It will absolutely save you time etc. Are you ok with a 'non-custom' control panel? If so, then go for it knowing, and this is the case with not just bootstrap but really any of the frameworks etc. bloat. How important is bloat and download speeds to your users? If your going to be using say 75-80% of the components in bootstrap then the trade is probably worth the time savings IMO.

The other side of that, if you're never displaying tables, then why are you making the user download a few thousand lines of CSS etc. for those tables? It may just be me but I def look at the overall project and how much am I going to use and is it worth it?

The other option, throw it up with bootstrap. It's an MVP (Minimal viable product) that way. Then circle back and write yourself a custom solution. That way you haven't invested time and money into a custom solution only to see your cp crash and burn.

Yet one more 'issue'. They typically are 'as is' meaning, changing the styles while it seems to be something that should be simple, depending on the builder, you could and most likely will spend more time customizing the thing than it would have taken a competent dev and designer to just build from scratch. So, if you like it out of the box, go for it.

Sorry, I didn't really answer your question just kind of through a bunch of other questions at you. Just food for thought.