I'm biased so take everything with a grain of salt.
The OB starter is based on the QPD design, it is well made and it works very well BUT it requires major modifications to the inner primary chaincase and to the engine cradle. The starter kit by itself is about the same price as the Alton and comes with a new belt drive kit. OB needs your primary chaincase and cradle sent to them to be machined an operation that can take a few weeks of turaround. If the work needed to take the bike apart can be done at home, then the costs of either starter system is similar. The OB starter is on the bike for keeps unless the modified parts are replaced with non modified ones. A plus with the OB starter is an outrigger transmission bearing.
The Alton starter can be installed with ease, if you can change the transmission sprocket, you can install one. There are NO modifications to the bike, the starter can be removed, the original parts put back in and no one would know it was ever there. The Alton comes with a new alternator which is a plus. It is NOT compatible with ALL belt drives, depending on the design of the pulleys and the width of the belt, it may not be possible to install the belt however it is fully compatible with a stock triple chain setup which has been proven to work very well.
I don't know what the lead time is on the OB starter, Alton has a hard time keeping up with demand so there is a two month lead time to get one but since installation takes half of a rainy day, you don't have to plan to have your bike strewn all over the garage for weeks.
So there you are, "you takes your money and you takes your choice"
Jean