It doesn't take that long to get the xp to unlock stuff though. When the jackal came out I had 0 xp because I had just bought some of the other class unlocks, and it only took me a week or so of casual play to get it unlocked. I did have the veteran bonus from buying a cheap booster pack way earlier in beta, but even without that it wouldn't take too much longer.
The special XP awards for the various badges combined with the bonus xp for the first win of the day can get you there even if you only play a couple matches a day.
I have to agree with the Jackal>Spinfuser though. The stealth spinfuser is decent, but weaker than all the other spinfusers. It's probably better than the jackal in an open field engagement as long as you can aim good (and its ammo lasts longer), but the jackal is better for the kind of situations I'm usually in playing infiltrator - snuck up on a guy standing still and need a way to take him out quick. Before the jackal it was run up and melee him in the back, with the jackal I just fire three of em onto his back and boom. With the spinfuser I'd have to shoot and hit him directly twice, and usually he'd move after the first shot. It's also funny to throw three down on top of a hill that everyone skis over and blow up people as they go by. In one match I just sat there the entire match getting one after another, wound up with 30 kills and only 2 deaths - the sad part was I never even had to change hills, the same guy would come flying over the same hill he blew up on last time and boom again.
Can even stealth kill heavies with the jackal. Stick three to their back followed by a sticky grenade. Sticky goes off as you set off the jackal, boom. Without the jackal I'd have to tag them with two sticky grenades, or backstab them twice and hope they don't react too quickly (usually worked, but occasionally they'd jet away right before the second swing went off).
Not sure about the whole Spinfuser>SMG though. Indoors the spinfuser shines, but if you can aim it the SMG is great for shooting down flying folks outside. I've seen people who were good at aiming it just mow down one guy after another with that thing.