No problems with light switching modes while on a bumpy road. I did several hundreds miles with this light attached + 700 miles trip with the light on the bike on the bike rack...Very solid.
As far as price goes, I saw older model MagicShine for around $80, and you can buy the one I have ( copy of Magicshine, and probably made by the same company ) for around $30-40 on auction or around 40-50 "buy it now". It comes with bicycle mount ( I replaced mine with the original MagicShine mount - $7 in parts for mount and rubber rings ) + head strap mount and battery. The one I got have only 2 cells comparing to the original MagicShine battery with 4 cells. On high I'm getting at least 1.5hrs on high when it's around 32F. When is warm, you can get 2-2.5hrs on high. Extra battery pack is around $7 if you buying it from the same seller that I bought my light.
Some good tip, plug the hole with some silicone where the power cable goes inside the light head...This way this light will be pretty much waterproof. I did that and I was driving 300 miles ( around 5 hours ) in a pouring rain...no issues.