There's no right answer (hence the deafening silence!), but getting in a few hilly MAF runs each week can always be beneficial. I do two treadmill runs a week to balance out the fact that every outdoor run I do is very hilly. The part that you're really missing is the downhill element which is really an important piece of MAF training. Do you have a negative incline option?

There have been some elites who have employed propped up treadmills for marathon training, very successfully. However, indeed you should be very careful.

My standard treadmill workout is the following: 10 minute easy jog warmup, 5 minute walk @ 4MPH@ 15% grade. Every 10 minute run session I up the pace just a tad, maybe .5 mph. All the walk segments stay the same. I will up the running pace until I hit my upper MAF HR and stay there. My shortest workout is an hour, but sometime I will go for 2-3 hours if the weather is really snowy and icy out on the weekend when I do my longer runs. A couple of weekends ago I did this workout while watching the Pats game. FWIW, I am an ultrarunner so this workout suits me just fine and gives my legs a break from the roads....it's also perfectly suited to a trail ultra where you walk a lot on the hills. It trains my legs for running and walking! The other benefit is breaking it up like that makes the time go by faster. If i were going to run hill repeats, I'd find a good hill outside and do them there. I probably do this workout on average once a week at this time of the year and very rarely in the better weather. Steve