I also don't think this should be the point of a BJ only session unless the SP can really provide that. (which Julia can, because she is a super hero LOL and I do admit in a duo session it's way easier)
This has mostly been why I feel more wary of providing that service lately, because some people expect a blowjob the whole time or without hands or really unrealistic things like that. They don't read my restrictions and expect FF, etc. I initially offered that session because people were asking for it, combined with a massage, and I received a lot of gratitude.
I took the session away, then I brought it back last winter because I had an operation that prevented me from having penetrative sex last winter and it kinda stuck even after I had healed. But I do find that although it's straightforward and my cheapest option, I always get a TON of questions about it with answers that should be pretty obvious. It became more tedious at some point, I'd get people who hold themselves back from climaxing and who want a 40-45 min blowjob or longer. They would push boundaries and basically treat it like GFE without penetration or even PSE without penetration, etc. A lot of people just do not understand that I am not a PSE provider.
I did have some really good sessions.

I had some clients who took the option to see if we would click before getting full GFE, and they were sweet. I had clients recently who fit that description that I really liked. I also had one or two clients on the kinkier side who I vibed with a lot more than I anticipated. I just don't like feeling like I'm a suck-machine.