I agree with the others - there is absolutely no need to buy a dedicated diabetes kit bag. I have been on hundreds of flights since starting with insulin and never spent a penny on a dedicated bag apart from a couple of Frio wallets for travel to hot climes.
That said, I only ever use one carry on bag - two would need to be carried so would just get in my way. I can fit a Kindle, phone, change of underwear, snacks and multiple weeks of diabetes kit in a single back pack so see no reason to make my life more challenging.