I bought a Robbe U-47 which is still a couple months from seeing water. I was in your place a while back and was severely tempted to get the Subtech Albacore, since I'd be able to reuse it's WTC in a U-boat or fleet boat hull at a later time. (That WW2 era sub is my favorite.) I also did not like the dynamic diving aspect of the Robbe, which is almost as toy-like as its little paddle diving control mechanism. (yuck)
But I went for the Robbe for 3 reasons. First I really wanted a U-boat and did not want to start out with anything else. Secondly I did not think there would be enough reserve bouyancy in the Albacore's WTC to float a U-boat hull high enough in the water for my tastes. And last is that I got a good deal buying the kit plus the 750ml Engel dive tank plus a pitch controller.
There's a lot of building with the Robbe, so on a budget go with the Albacore, unless like me you just have to have a U-boat.
I have also done some upgrading: I did away with the stuffing tubes and instead got some 4x11 mm shaft seals and got some 4x8 mm teflon sealed ball bearings which are normally used for electric cars' axles. I used different (imperial) sized brass tubes from my local hobby store to make handy little bearing holders and shaft seal holders. I also used the Dremel to open up the standard shaft supports just a little so they have bearings tacked in with a drop of CA.
Also I had the stock motors swapped for Johnson 540 ones which only turn about a third the RPMs. That eliminates the need for an expensive gear reduction unit. Of course I'm talking out of school because my boat is still in pieces on the bench.
I also got brass props and an Engel BTS and will be sealing up a servo to run the front planes independently. Instead though I may just attach another control rod to the rear planes and then run it forward to operate the front planes simultaneously. The linkage would snap together under the front deck, which is also where you would adjust it.
One thing to note. The Robbe would be best served by a one liter dive tank, but no one makes it. The 500ml fits well, but I hear the water line is very high. Better is the 750, bit it is a little bit of a struggle to fit in. It doesn't want to fit perfectly straight, and as the tank fills, the long bolt comes out just as long as the tank itself, so you have to have somewhere for it to go. That necessary void will be "reserved" in my WTC by a flared brass tube mounted off the end of the bolt. That way wires and crap can fall on it without potentiating any underwater disasters.
I've got some pics so far, if anyone's interested. There will be a formal writeup later. God only knows where the batteries are going. In fact I'm going to go post a question about batteries right now...
If you want to see the pics, let me know and I'll post them on my site tomorrow.