I would run the other way from in-mast furling, for the reasons mentioned above and:
1. noise at anchor from wind whistling in the slot
2. "Operator error" most likely at most inopportune moment
3. lack of battens making sail shape a nonsense term
4. lack of battens making sail noise (flapping) and wearing sail out sooner
5. vertical battens (if you have them) that WILL poke through their pockets and get stuck inside the mast
5. reefing keeps sail area high on the mast when you want it there least
6. how to fix things that jam 20' up in a 5' sea (it won't jam when it's flat)
It sounds to me that though many people may profess to enjoying their in-mast r/f systems, they're like the fox who lost his tail in the trap. Boom-mounted systems, though they may have some of the same and other issues, seem to make much more sense.
I have a very similar view to Vasco and CD on this. I used to think in-mast furling mains had many potential problems and drawbacks. Now that I have one (obtained with much skepticism and thoughts of "we'll see what happens"), I've changed my tune. It is true that you lose sail area. That's just one of the trade offs you need to accept. We have vertical battens, so we have some roach, but it's not the same as a traditional roachy main.
Likewise, I still am waiting for the first jam when trying to furl or deploy, but we haven't come close yet, and we've used the system in a few less than ideal situations (e.g., reefing on a beam reach). But when it happens, I'm sure I'll curse the thing.
I'm posting this as a reply to PaulK's post because I think he pretty much hit the highlights of the perceived disadvantages, and he's not wrong. That said, I do think some of the stated concerns are overblown:
1. Noise at anchor. We haven't experienced this at all. If the sail is not in the mast, then you can get some noise from the spindle inside the mast clanking around if the boat is moving. We take the sail out only for winter storage, and on land the boat's not moving (hopefully), so we don't view this as a real problem.
2. Operator error. This is true, but it's also true about so many other aspects of sailing, even on boats with traditional mains. For instance, battens hanging up on lazy jacks, engaging tranny with a sheet in the water, getting on override on winch somewhere. I do agree, a furling main does add one more thing for which operator error can cause a problem, but it's one more thing, it's not a new concept.
3. True dat.
4. Only half true. Traditional mains flap too, and many traditional mains don't have full battens.
5. I don't have any experience with this, so I can't really comment. I will note that if you are right that battens poking through the main is a real issue, it would be more difficult to inspect on a furling main than on a traditional because the battens do not regularly come down to the deck where they can be viewed easily.
5 (your second "5"). True, but overblown. You are lowering the center of effort on the mainsail when she's getting furled, but you also are keeping weight aloft with that portion of the furled main that remains high on the mast. But you are right, as compared to a traditional main the center of effort is higher when reefed.
6. Again, I think you are right, and it's one of the disadvantages.
Don't underestimate the advantages, however. And several of those advantages fall into the safety category:
First, you are more likely to reef and reef early because it's easier. Don't underestimate this. How many times have you delayed reefing because it's a hassle, and then you find yourself on deck hanging on for dear life wrestling a malevolent mainsail? That's a much more dangerous place to be than in the cockpit furling up a mainsail with less than perfect shape.
Second, and similar to the first point, you can change gears much more easily, which means you are more likely to have the right amout of sail up more often. This applies to shaking out a reef too; think about the number of times you left the reef in even when the winds lightened simply because you didn't want to bother with the reef.
Third, because it's easier to deploy and reef, you are more likely to use the main, and frankly, more likely to go sailing.
Fourth, it's just plain easier, and if you're cruising, particularly short-handed, that counts.
Fifth, you are not folding the sail, so you're getting less wear (though this might be offset by chafe you might get when furling/unfurling the sail).
Sixth, the sail doesn't collect water when the boat is not in use.
Anyway, there is no doubt that there are plusses and minuses to furling mainsails, but with the advent of better furling mechanisms, vertical and/or inflatable battens, the scale tilts are lot more to the plusses today than it did 10 years ago.