The JP SLW is very similar to the SB Ultrasonic.
Both work great with 8/9 sqm sails.
I've sailed both the SB Formula 161 (4 years) and the SB Ultrasonic (only recently).
The formula goes better upwind, the Ultrasonic feels very light and is faster for me on a beam reach.
I've also posted my experiences on another good thread: http://www.star-board.com/forum/showthread.php?t=13384
I agree that a Formula is not that difficult to sail as long as you stay in the 8-12 knots windrange.
When the wind picks up to 15+ knots and also the chop increases, I can assure you that it becomes "very hard work", especially if you are still learning.
Because you said that you just started windsurfing, I think a formula is not the best board to choose.
The ultrasonic would be much better. It's a feather compared to your Funster 180.
But I agree with Roger that it is more important to get yourself first a larger rig, say 9 sqm. It will also work just fine with your Funster.