So... first one I bought didn’t work at all. Had to take it back, so advice is buy from boots or another shop, not online, so you can exchange it easier.
They also sell different size attachments. I’m a DD and the middle size worked best, so not sure if size is an issue. I would say make sure you have a snug fitting bra on. This will help.
They come with two sizes already in the pack, medium and large. Suction didn’t work on the large for me, even though measurement wise I should have been better with the large, hence you gotta try out both.
I did have a hand held for emergencies. All electric pumps can have issues, so it’s handy to have a spare hand pump ready whichever you choose.
Ultimately, being able to pump ANYWHERE is amazing. Though you have to stay upright, so doing laundry, anything requiring bending down is out, but you can’t have it all! Plus, you have to keep checking to see how full it is, as you can’t quite see. It was a small price to pay for the ease of being able to wander about, eat dinner whilst pumping etc.