I've also tested the new v3 site and I've tried my hardest to break something, but to no avail. It all worked very smoothly, bar the brief moment when I though I'd been given an empty private key because I imported it as legacy (force of habit!) instead of segwit. Also very nice that you can split deposits up in to multiple different vouchers.
Oooohh! That happened to me as well, except I wasn't smart enough to realize this by myself. Thanks o_e_l_e_o!
@ChipMixer: Please disregard the PM I sent you, importing the private keys worked just fine after reading o_e_l_e_o's post above. Smartass that I am I didn't click on the "Import to Electrum" button but directly copy / pasted the private key from the "Withdraw" page. Also of course I didn't read the note about Electrum requiring a special prefix. Maybe put that part in bold? Not sure. Either way I didn't realize there was new information on that page, blinded by routine I guess.