[Rob Stehlik]

In the past 4 years I have been involved with the team, 610 has used 25 chain on our drivetrain 3 times. We only popped a chain off once. Alignment of the sprockets is crucial, but not really that hard if you design it in. Strength does not seem to be an issue, but larger sprockets lead to lower tension in the chain if you are concerned. It's hard to say, but the "stretching" one sees with 25 chain may actually be wear in the aluminum sprockets. In recent years, I have noticed the sprockets from AndyMark are made out of thinner sheet metal without any chamfer on the teeth. It looks like they are just cut on a waterjet. I'm sure this reduces their cost of manufacturing, but I liked the thicker ones with chamfers to guide the chain, and I suspect they would not wear as quickly since the base of the teeth was wider.
The real benefits to 25 chain are lighter weight and smaller size. Also, if you get the "dark soul" chain tool, making chains is really easy, with no more master links! It's actually much easier to work with than 35 chain.
Depending on the application, I would be hesitant to use 25 chain on arm joints and other heavily loaded mechanisms. Our flipper arms this year were powered by two 25 chains, and they broke a couple times. I think the shock of driving over the barrier or pulling the bridge down was more than it could handle over time.