They're pricey but will last forever. So to me, it just depends on your style of play. If you only use it as a transitional bag while you are learning and adding more discs to your bag - it will outgrow it before you really got good value out of your investment.
However if you are mostly just a casual player, playing quick rounds for relaxation and don't want to be burdened with the extra weight - I would go for it.
To me, they are ideal for casual players to have something that will last, and look "cool".
Not that you can't play tournaments with a NutSac. However having something a little more spacious and conventional is better(extra room for scorecards, pencils,towels, sunscreen,bug spray, etc).
I opted for a FADE crunch box because I wanted to have the extra room for misc. shit and a water bottle.
TL:DR = If you are just starting out and that's why you have limited discs, Get a Crunch Box w/ Straps. You can always upgrade the bag later and keep the straps. If you are damn sure you just like to use a handful of discs for the foreseeable future and like the style of the NutSac, get one.