To be honest I'm not a big fan of the H&M style of nursing top (cross over top with 'modesty' panel insert with nursing openings) as when baby pops off, your boob is sticking out uncovered and when feed finishes you have to unpost your breast through the hole before you can clip your bra up. Plus the neckline stretches when you move it to access the openings.
If you go top up/vest down or top up/cardigan around then when baby pops off the top falls down to cover you and you can reach down the neckline to re-clip your bra.
If the nursing top has a under layer with nursing openings check they are actually where your breasts are. I bought a Mothercare nursing top a while ago and the panel had openings at either side of the waist. Also, the panel was attached at the sides to the top so if I moved the openings to where my breasts are, the top was pulled up so all my back fat was on display. Not what I call discrete 
Here are some pictures of the types of nursing openings.
The easiest (IMVHO) to use are 'Front Layer Access', 'Cross Over', 'Empire Line Access', 'Vertical Centre Opening'. These ones you could sort your bra out before getting baby in position and lifting nursing panel.
The 'Wrap Access', 'Pull down/Pull aside neck line', 'Inner/Interior Layer' all seem to be the kind where I might struggle to get my breast covered quickly after a feed and that you would have to faff about posting breast through hole before being able to feed.
I'm odd in that I don't mind a flash of breast whilst getting baby on but I hate the thought of struggling to tidy myself up after a feed or having to get breast out before picking up baby as some of those types of openings are impossible to get your breast ready (bra cup down/breast through opening) whilst holding baby.