The original Roller-Furler for the 192 and 222 was the old Schaefer model 100, this was designed for boats like the DAY SAILER, although the small jib o nhte 192 would most likely still furl OK. It was DEFINITELY too small for the 222 (and that opinion comes from Schaefer). The main problem with this type of furler in general is that it used a wire luff in the jib to roll around, instead of using a foil over the forestay. These "wire-luff" furlers were the old-style furlers and the idea had been around for a long time. They work OK, but can not be used to partially furl the sail to "reef". They do not allow yo uto put enough tension on the luff of the jib to get a good shape to the sail, they tend to sag off to leeward tremendously. For casual sailing, that isn't a huge problem...... but for racing or performance cruising, well it really hurts windward performance. They can also get tangled with the forestay as they furl/unfurl, since the forestay and the jib luff are sharing the load, if you tighten the jib luff too much (possible if you have hte optional jib halyard winch) it causes the forestay to sag, if the jib luff is too loose then it will sag. The newer jib-furlers that have a foil (plastic or metal) that fits over the forestay with a groove to take the jib luff allow the forestay to take the load and the jib is supported along it's full luff giving much better shape to the jib. Partial furling can be used to "reef" the sail, although unless the jib is made for this, reefing really doesn't work well since as the sail furls, it gets fuller since a sail is not flat and the shape sewn into the jib does not roll up uniformly. Not a big problem off the wind, but this limits use of the "reefed" jib for windward work. (Full sail holds more wind and increases heeling while reducing forward drive.)
For casual sailing, especially if trailier-sailing, the wire-luff furler makes rigging/unrigging easier since the jib can be lowered as a "sausage" and removed. The over-the-forestay type furlers are harder to remove the sail, so you almost need to leave the jib on the furler while trailering. The furling drum will also usually cover the forestay turnbuckle.
I keep my boat on a mooring all summer, so if I added a furler (unlikely on a DS II, but not out of the question!), it would be one that fits over the forestay. But if I trailered, I'd probably go for the wire-luff style. On a 192 or 222 it would be possible to upgrade to a larger size wire-luff furler, you still could not "reef", but furling the sail would be easier than with the under-sized original setup. Cost would be less than replacing the Schaefer 100 with a over-the-forestay furler (especially since jib would not need further mods), although the CDI flexible furler is not much more $$ than either a Schaefer or Harken wire luff setup. Also the Schaefer Snap-Furl is not that much more $$ than the CDI. If you keep the boat rigged for the season (mast stays stepped), the over-the-forestay furlers are a big improvement in both furling ability and sailing performance. If you trailer and don't mind the reduced pointing ability of the wire-luff jib....... stick with that.
If, like me on my DS II, simplicity is desired and needing to instantly furl the jib is not important....... switch to a hank-on jib. A partially furled ("reefed") large roller jib is not equal in performance to having a choice of 2 hank-on jibs (genoa and working jib), but it is more convenient and most likely much less $$$.