IME the Underground Accelerator is better on bass that the other Alembic F2B style pedals I have.
I have used an Alembic F2B in the past and loved it. I was using a
@johnk_10 FET-F2B that is wonderful and clean for many years on my pedal board, it is on my second board now. My first SB was a mini tube Particle Accelerator that I use in my recording set up. Now I am using the Underground Accelerator because it is more versatile and has a nice depth and heft. The UA in low gain settings is just as clean but has a bit of depth over the PA to my ear that really works live plus the ability to push the gain for grit is a plus.