The Kirby Morgan M-48 is a good choice for technical diving as the lower pod is removeable and allows you to breathe off a stage, deco bottle or buddy's reg. It eliminates the need to carry a backup mask in the event of a reg failure. In my experience most FFM divers do not carry a spare mask and consequently, as James points out, life will get interesting for them in an emergency.
Most PSD divers will vote for an AGA and a few PSD divers will state that if they are suitable for use under PSD/commercial conditions, they are by default excellent for recreational purposes. That is like saying the FN-FAL in my closet is an ideal hunting rifle because it was a great battle rifle used by the armed forces of over 90 countries. I like my FAL and it probably gets shot more than anything else in the rack, but it would not be my first choice in a hunt of a lifetime situation. Similarly, the AGA is a nice FFM, but it may not be the best suited to an recreational diver's individual needs.
The Mantis is very similar to the Scubapro FFM and both are good choices for a recreational diver, although you will want a back up mask with it.
I have never heard much of anything positive about Ocean Reef FFM's, but I don't have any direct experience with them.
The original Cressi style mask is still available for about $75 online. They get the jo done but visibility is limited and they do not have a separate oral nasal cavity and that can result in elevated CO2 levels. On the other hand, you can still use the mouthpiece on your regulator with the mask, so during periods of heavy exertion you can avoid the elevated CO2 issue.
Some potential pros are:
1. Nice to have in very cold water.
2. Allow the use of communications equipment.
3. Won't let you drown if you Oxtox and convulse.
4. They prevent jaw fatigue.
Some potential cons with FFM's are:
1. The strap system can feel a little confining under some conditions.
2. Some designs, AGA's in particular, can be very bouyant requiring an add on weight kit.
3. Some FFM's use dedicated second stages that require specialized service and this can be inconvenient if you do not have an authorized dealer nearby. Other FFM's, Scubapro, Mantis, etc, use your own off the shelf regulator while still others, Kirby-Morgan M-48, etc, are available with a dedicated reg or can be used with your own.
4. As indicated above, most FFM's require a backup mask in the event you need to switch to an alternate gas source.
5. Some FFM's are sold with a positive pressure regulator. These have advantages in some PSD and some surface supplied commerical situations, but for the most part for a recreational diver they noticeably increase gas consumption and offer no advantage at all. AGA's can be purchased in both positive pressure and demand versions and if you get swayed to the AGA route, get the demand version.
