I have the Apidura frame bag and have no problem getting to the front bidon but have had to use a smaller bidon on the down tube. If you have not found out yet, these bags are not waterPROOF. So if you are putting anything electrical in them, use a plastic bag. They make 2 types of seat packs. One is water resistant and the other one is waterproof, so get the right one.
I found the seat pack a pain to get into and so I am now using a Bridge Street Saddle bag. It has been on the back for over 1000km and I dont know its there and is totally waterproof. Its far easier to find my gear than the Apidura and has more space. The Apidura swayed about a bit unless you fastened it on very tightly and then you restricted the loading space. I much prefer the Bridge Street bag.
http://bridgestreet.cc/