I agree with ameyam in that many engines do not respond well to hand starting and some manufacturers reccomend electric starting only on some types so a well rounded flyer that is likely to have many various engines definately needs an electric starter and perhaps more than just one the meet the needs of a variety of engines.
Having said that Marshrabbitt you have have lots of excellent advice on the operation of an electric starter as well as the need for proper priming before using the starter and so on. You have two excellent starters that match any direct drive units out there. The only thing lacking is is voltage. If you supply only 12 volts the starter is hamstrung even if you use automotive or tractor batteries. Ugh, who want to lug one of those things around.
For our use what makes all our starters come alive is voltage, voltage is indeed king for our use.
You are lucky the ten dollar battery is back, it will spin your 75 heck for that matter a 120AX like there is no tommorrow:
On sale agine
http://www.harborfreight.com/18-volt-battery-67029.html
The coversion is so easy an nothing beats it for all around use.
Here is your Hobbico 90 among others of mine. There is an even an easier way to attach the battery to your Hobbico 90 using just a plywood plate and RTV that works well on ones I have done since this one for other folks.
John
having said that
http://www.harborfreight.com/18-volt-battery-67029.html