Cigarbabe: Never had a bottom feeder mod or ever worked with one, but that might be a good idea to avoid small "filling" issues. Does the bottle screw into threads on the mod or insert in some way? Easy question and I guess I should know, but I still use old equipment.
NEWQ: could you say what state you friend lives? Maybe there would be a "brick & mortar" nearby where he could try different styles? Sometimes working directly with something is the best method to meet individual needs.
I apologize but i was not the original OP Nikinic was the one with a friend in need. SOrry for the confusion.