Hello FunkyGuy,
As marso mentioned, you should definitely consider purchasing an actual pick set. I bought a 14 piece set but as many have mentioned in the past, even a smaller set with only 5-8 would suffice. If you could afford it, get the jacknife and a 5 piece set at the same time (save on shipping later on). I don't have a jacknife so I have no idea how easy they are to use but I would imagine they'd make it a bit difficult to get feeback from the lock when picking. With the individual picks, you should be able to pick locks easier/quicker than with the jacknife.
Between the 2 jacknifes, I personally like the aluminum model a lot. Something about nice shiny metal makes my eyes glow.

Is it really worth paying the extra 10 or so dollars? Well to me it is but that's just my opinion. I would think it would be more robust than the fibreglass one but again, I'm just guessing. If you're going to use it as your main pick(s) then I would go with the aluminum (if it indeed is stonger) or go with the fibreglass if it'll just be a backup. Perhaps someone else will add to this.
Eventually I wouldn't mind having one myself but I've just recently purchased the MPSX-14, 3 extra tension wrenches, Brockhage pick gun (plus extra needles for it), and a SouthOrd 8 tubular pick.
Bottom line is, if you can afford both the aluminum jacknife and a pick set, go for it. I think you'll be happier having both. If you're a little tight right now, maybe you can get the fibreglass model (cheaper) and the difference in price from the aluminum one you can buy a 5 piece pick set.
The choice is all yours. Good luck with your decision and keep us posted how you make out.
hmmm...nice shiny silver
