It's good - as long as your running is ok in trainers and you feel you don't have the willpower to just run further or faster. If you're crap in trainers then don't bother with boots. Personally I'd just run for longer.
If you feel you must, then make sure they're broken in properly or you'll have blisters that will take ages to shift and will therefore set your training back.
I know i'm a bit late on the thread,
but i also run in boots (cue the anti running in boots brigade) but as angry doc said if your techniques good and you're fit enought and they're well broken in you'll be fine,
also look at the lacing technique, lace up the bottom 3 eyes and the speedlace lock as normal, cross over to the the opposite lug 1 row higher, then take the straight us the remaining 2 eyelets, the lace from top back down to the ankle in the normal criss cross manner, result, more ankle support and less constriction on your shins, ie lower chance of shin splints, cant lace like that in basic i've been told, but for doing your own runs give it a try.
Also fill a rucksack with 30 kilo's of kit, and take a naked hike in the middle of the night wearing nothing but boots and some EMS Shorts, (these contract your muscles involuntarily) so you take a step and your leg locks out and you fall over if you can take that beating, make it a full 20 miles in 4 hours, get home and pull the thorns out of your shrunken member you may have what it takes to either be a bootneck, a legionaire, or be assigned to mental hospital hope that helps you with you booted runs