Jiffy reefing is better for a number of reasons. It is easier to do. Roller-reefing can be a nightmare of easing the topping lift, holding the boom up, pulling the leech out, easing the halyard and hanging on (in conditions that warrant reefing) while someone cranks a little handle up by the mast until he drops the handle overboard. Jiffy reefing is also faster. You ease the sheet and halyard and start trimming the first (or second, or third) reefing line. The mastman hooks the new tack in place at the gooseneck, and the halyard is tightened back up. When the clew is where you like it, you trim the sail. It is safer, since only one crew is needed at the mast- no one needs to hold the boom or stretch the sail along it. There is less equipment to break - jiffy reefing uses lines, blocks, winches, and halyards that most boats already have or are simple to rig. If the reefing handle cracks or goes over the side, is there a replacement? What if the gears inside the boom get stripped...?
All that said, roller reefing can and does work. Perhaps you can look into jiffy reefing later, when you need a new mainsail. For the vang, talk to a rigger or a REAL chandler such as Hathaway Reiser & Raymond in Stamford, CT about getting a jaw, or claw, so you can vang the boom down even if it''s reefed. It''s a C-shaped thing, about a foot or so in diameter (the rolled sail has to fit inside the C, along with the boom!) often cut from aluminum plate with plastic rollers on the jaw ends, to protect the sail. The opening is just a few inches across - big enough to slip over the mainsheet and then it goes down the boom, with the jaws up. There''s a shackle on the side opposite the opening, where you attach the vang tackle; it is generally led to the toerail or a padeye on deck. In theory, you roll in your reef and the sail slips past the jaw and around the boom. You then tighten the vang. I looked in the Defender Layline, and Harken catalogs and didn''t see any of these things, so perhaps posting in the classified section here, or going to a nautical flea market would also work.