Currently, there are only 2 kits on the market for Akula's in 1/350 scale, Bronco and Hobby Boss. I have now built both kits and can say the Bronco kit is more accurate than the Hobby Boss. Here are the inaccuracies in both kits:
Bronco: Length is that of an Akula I. Diameter is slightly bigger than actual Akula's.
Hobby Boss: Sail is way too tall. It should not go past the height of the towed array pod.
The Bronco hull is slightly more difficult to build since it is in 3 pieces vs the Hobby Boss 2 pieces.
Because the Hobby Boss sail inaccuracy is so noticeable and cannot be fixed, the Bronco kit beats the Hobby Boss kit. If you want to make the length of the Bronco accurate, you will have to kit bash it with another Bronco kit. There is nothing you can do about the diameter, but the bigger diameter is not noticeable unless you have the Hobby Boss Akula next to it.