Get some Sennheiser HD-25's - not only are they the industry standard in pro sound reinforcement but the BF has plenty of juice to drive them.....I've not come anywhere near running the BF headphone vol above "0" with a pair of these.
Re BF instrument input if you can only afford an audio interface then go with the BF but don't expect the results of superior equipment - the BF is great no doubt about it, but expecting it to achieve results above the design spec & price-point is totally unrealistic.
All too often now in this product over-saturated "electronic/computer/recording" industry consumers (& clients, many of whom should know better) spend £500 & expect the results of gear that cost 10 times as much, plus the £500 piece of gear should also make good coffee..........you get what you pay for!!
The BF is an excellent 2 channel portable audio interface - it's stereo channels sound great & the feature package is better than anything else of similar design, you would however get better results using a dedicated high-end DI to input your instruments - just as you would on a FF800 or UFX or any other audio interface.
If all you can afford is the BF then do get it but please be realistic about results vs. your budget.