I have one I keep under the seat of my Wee and I used it to start a V6 motor that had sat for a couple of months and the battery was showing about 2volts, it worked, only just but it did work, I did have to hook up the jumper battery and let it sit for a about 4 minutes before it would do the job, I believe it would start a bike without any problem.
But with the technology used in these batteries you can not run your bike off the jumper battery after it has started, it will start a chemical reaction in the battery that could become dangerous, draining the battery too fast or charging it too quick will kill it.
I have one that belonged to a mate, it failed to start the car and he did hear a crack come from the jumper battery at the time, when he put it back on charge it would never get the charged full light to show up so he left it to charge for about 12 hours and the battery overheated, expanded and forced the outer cover to blow open.
PS; with mine I had to make a cover for the switch so it would not turn on while under my seat and not in use.
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.