Hello my friend!
True the Double Agent is slow, very slow and some of them do whistle; not mine, btw.
That's how far we agree.
Not stable? You mean in pitch? True the first model is a bit pitch twitchy and not easy (the first sessions) to get the height right. I solved that by changing the stabilisers' angle of attack (returned to original after having dialled in). The 2017 model, due to its longer fuselage is very stable and noticeably faster (due to the thinner mast I guess) and nearly as manoeuvrable. I suggest you try it; you might reconsider your opinion.
After having tried several other boards, the low volume of the DA board makes it the easiest to waterstart of all the ones I've tried.
BTW, I know a couple of riders who bought freeride hydrofoils which from reviews were considered easy (of the Fone freeride kind). They nearly gave up hydrofoiling till they were suggested to have a go at the Double Agent before giving up. A few sessions were enough to get them going.
I personally managed rides of 500 meters between falls after 6-7 short sessions totalling 2 hours, and I'm an old dog who's not supposed to be able to learn new tricks. Two weeks ago, a Belgian rider bought a 2017 DA over here and in less than a week (after about 8 sessions totalling 8 hours) could gibe, ride toe-side and even tack (surface). More remarkable: he came straight from twintip without having ever ridden a directional.
I haven't tried the other beginner's hydrofoil with similar features (large wing, alu mast...) there is no reason they should behave much differently than the Cab DA.
The DA is turns and carves like no other. I enjoy riding it a lot more than my faster and quieter Zeeko Green & White, which is considered as one of the best for beginners and more advanced freeride hydrofoil. I know several experienced riders in Bali and Hua Hin who wouldn't consider upgrading because they love playing and carving in the waves, something you cannot do with fast foils (ask BRM Greg).
In the end it's the sort of riding style that determines your preference for such and such a foil. If you like zipping along at high speeds, the DA isn't for you. If you enjoy foiling like do when flying a Piper Cub or a floater hang-glider, then it's definitely for you, even when past the beginner's stage.