with my twin brothers we always used blankets to prop up their bottles when feeding them at the same time. One of my twin brothers had colic and was a really fussy eater and had to be held most of the time or he wouldnt eat, and he'd only eat for my mom and not me or my step dad. So it came in handy being able to put my non fussy brother in the boppy or bouncer and prop up his bottle if my step dad or i werent home to help. The only thing i don't like about the bottle sling is that they have to be in their car seat to feed them, i wonder if it would work in a bouncer that has the play bar on it? Sorry i didnt really have any helpful advice but i would try the blanket trick before buying a wierd device to do it, just to save money if nothing else. Twin boys are definitely an adventure! my brothers are now 10, its hard to remember they were ever that little lol
I don't have any experience with either one (or with feeding twins for that matter), but just wanted to send out my sympathies. I know it must be hard to never get more than an hour and a half break, especially when caring for twins!! On the bright side, at least they are eating on the same schedule - I imagine it would be much worse if they were not.
How old are they now? Do you mean it takes them an hour and half to actually finish a bottle, or an hour and a half for the entire process? Are they eating formula or pumped breastmilk?