I've not used the MEFO's but most reviews are good .... although I did read a long term report from a guy doing a big Mexico ride who did not like them in terms of handling. But most reviews I've read are positive. I did a dual sport ride with a guy on a KLR that had just mounted them. He did fine and said he liked them on the rough dirt roads we were on in California Sierra.
Mileages are reported to be good:
8 to 10,000 miles on a front, 6 to 8,000 miles on the rear. This is really good mileage from a 50/50 tire. But if you have a heavily loaded bike and ride at speeds over 70 mph, then your tires may wear out quicker. So as they say YMMV.
I thought seriously about MEFO's last time I bought tires but can't resist the price of the IRC GP-1's. Also, the Shinko's look very good and they will be on my list to try out. On a Baja trip over a year ago I started with street tires and hauled two tires along. The front was a very expensive TKC (about $80) the rear, a cheap IRC ($60) This combination was OK once the TKC wore down a bit. Street handling at first was "unsettled" to put it nicely! Off road I love the TKC on my DR650. Good in deep sand, and good control on very loose and steep downhill, off camber "roads".

Here you see the worn Pirelli Scorpion MT90 AT on my DR with the NEW IRC GP-1 mounted on the rack. At this point I had already put on the TKC (you can just make it out) which saved my ass on the other side of this hill!
With the GP-1 IRC in Baja trip and I rode for about 1000 miles, mostly off road similar to pic. Then rode home (highway to San Francisco) and put a bunch more miles on it doing mostly hard, high speed miles on tarmac.
I changed it out at 5,200 miles according to my tire log. Not bad for a $60 rear tire.
My front TKC was removed immediately after Baja with about 2000 miles on it. It still looks like new. I have two sets of wheels so swap out tires/wheels depending on ride coming up.
Here in the USA the MEFO's cost about $125 REAR, $85 front, plus shipping.
If one is intending to ride into remote countries for extended periods of time/distance with no tire re-supply available, then something like the MEFO or TKC are ideal. They are versatile, and work in a variety of terrain and most of all, they LAST a long time, even on pavement.
If you do not need a tire for dirt riding then I would use another type tire.
If your dirt riding is not far away from civilization, I would use a cheaper tire than a MEFO. Many good ones for half the price. (Shinko, IRC, Kenda,
Cheng Sen, Maxxis and more)
Patrick