Yes, I've used it once with good results. I wrote about it briefly when I was trying it out this past June. https://www.arizonashooting.org/forum/viewtopic.php?f=4&t=8130&p=53233&hilit=guntab#p53233
Zelle and PayPal F&F are fine if you're dealing with someone face to face, or someone remote that you know and/or trust. When I used Guntab, I was trying to buy a gun from a guy in the midwest, and he had no reputation as a seller, so I wasn't willing to blindly send him a payment with no buyer protection. He could have been a scammer for all I knew. I just paid an additional 2.9% to cover the seller's fees.
The biggest downside is added time for the transaction. Most people haven't dealt with them before, so if you want to buy or sell a gun with them, the other party has to set up an account and verify their checking account. I think that took a few days. Then, the payment can be made into escrow, and I want to say that took a day to be completed. After that, the seller can ship the firearm. Once the buyer marks it as received, then funds can be distributed, which in my case took a couple of days.
