I knew your model since a long time.
I have a website where I present my works on subs and other models (wooden toys for my grandchildren), on this website Ihave a special page for links :http://www.sousmarin.kart-thiais.com/Liens02_update.htm
If you scroll down, you'll find your website
About your question for underwater sailing...
This model is really very new, even not yet finished, and I only used it once last week end. I have not a big experience of navigation with it.
It's fitted with an automatic horizontal control which seems to be efficient when the speed is more than 1/2 on the "throttle"
There is a small trick in order to get the bow planes more efficient : The battery pack is fitted on a mobile rack, when the bow planes are going to dive, the rack goes ahead ( +/- 2,5cm = 1"), when the bow planes are going up, the rack is going backwards. It really helps for a good control but you need to have a good speed.