COMPLETE waste of money in my opinion. I bought it thinking it would be fantastic but the nipple/teat on it is sooooo hard and horrible it is NOTHING like the real thing. My dd would not entertain it at all.
If it's that Tommee Tippee one then I tried it out of desperation after dd2 would not take anything else. It was certainly easier to get her to take that than the other bottles.
She never really latched on very well, and this remained the case for the 6 months that I breastfed for, so I can't vouch for how effective it is at mixing breast and bottle.
What I would say is don't just give EBM in a bottle to get dh involved. There's so much else he can do! And although I'm sure many people have got it to work fine, I always felt that it was easier to exclusively breastfeed rather than mix bottle and breast.
Of course if you have to, then you have to, but I didn't think it made things easier. Everyone's different - that's just my experience.