Hey Vernon,
It’s hard to compare an amp to an effects pedal. The Mustang is a popular small amp but like most modelers there are tons of choices. The Boss pedal has even more. The Boss Katana series amps have built in most of what your pedal does and there are tons of YT videos out there on them.

Vernon
It really comes down to what your need is and what you want to accomplish.
As my friend San Luis Rey said, the Mustang and Katana have a lot of choices and the Boss pedal also gives you those variations as well
I’ve owned a Mustang and also a Marshall Code amp – great amps but at the end of the day, I wasted time tweaking sounds.

I’m now using a Marshall Origin 20 tube amp, a reverb pedal and a Joyo American Sound for my OD. I’ll probably buy a Joyo British Sound at some point – that’s all I need.

Take an inventory of what you want to accomplish and judge wherher the Mustang or the Boss pedal will fulfill your purpose better