As ktmdad said wear shin pads until you get real comfortable riding with the flats. I rode for a whole season without them and the first half of the season my shins were a bloody mess, but after about a month of riding with them, I never hit my shins again. It takes getting used to keeping a bit of weight on them so you don't roll your foot off of the peddle. Your foot won't slide, but the peddle will roll and bang. Once you get used to it though you shouldn't have any problems with banging the shins.
This was probably just me, but I found that the peddle would roll back as I was going up hill and encountered a large rock or root. I would try to put the power down and the foot would roll off the back of the peddle and the shins would get beet up. I more than likely had my foot positioned too far back on the peddle contributing to my issue!. So to help try putting your foot a bit more forward on the peddle if you experience any of that. Good luck and happy riding!
Just finished my first ride on the combo and found it a major improvement. Much more confidence (i.e less pucker factor), better climbing ability (easier to stand & pedal), and cleared obstacles that I've never managed to clear previously.
In hindsight, I should have made the switch a long time ago. And for the record, I did try several LBS' websites before heading online - I'll always buy local (personally AND at work) if presented with viable options.