3pl warehouse for FBA replenishment, is anyone actually doing this at 2000-4000 units monthly?

I get the concept, store inventory elsewhere and send smaller shipments more frequently instead of huge quarterly sends. Makes sense on paper and everyone talks about it like it’s obvious but the actual coordination seems annoying?

Like do you manually track when amazon inventory gets low and then tell your 3pl to send more or is there some integration that handles it? And when amazon decides to split your shipment across four warehouses does the 3pl just deal with that or is it your problem?

The fees are fine, I’ve run numbers and it works for my margins. It’s more about whether managing a separate operation creates new headaches while solving old ones. The big names seem built for larger sellers and price accordingly so idk what the realistic options are at my volume.