Your description of the marlow vega could be used to describe the Allgear 11.8, but the Allgear is definitely larger. I am loving the Allgear with the RR Pro, HHXF, and the HC/Wrench combo, and I am currently getting the best performance I have ever had out of both the HHFX and the HC/Wrench combo. The 11.8 with some epi 9.3 gets my highest recommendation.
I don't know which version of the BDB you are running, but my recent experience with the elongated bollard version and the Allgear was not a positive one. The BDB basically locked up with this rope and wouldn't tend slack in anyway, shape, or form. It was a struggle to get it to flow up or down the rope, and it was so bad in MRS that I could barely descend. I actually pulled the BDB off the rope and used a taut line hitch to get me to the ground.
I can't speak to the adjustable BDB's compatibility with the Allgear 11.8, but if the elongated BDB is your main squeeze I would definitely be looking elsewhere...