i just got brought a X-sub by my GF for my B-day
it's fantastic, i couldn't find my fish tank so i spent 30 mins sitting on the toilet playing with it in the sink as soon as i got it lol
I'm trying to find my tank so i can use it properly but right now i have it weighted so only the aerial is out, it rises slow and makes control underwater much easier.
i found with my rechargeable AAA it was neutral with no ballast, but with the larger non-rechargeable it was lighter and needed 10 balls or so.