Electric or manual starter?
Warning: I will be biased on this topic. I have backpain and I try to save every kilogram possible. Electric starter is about 1.5-2kg more and I believe they do not add value.
You will probably end up with a small motor (80-130cc) and these are easy to start. So saving those 2kg for electric starter will allow you to take 2.5 litres more fuel. So I would rather have a slightly less comfort at the start and then have almost one hour more airtime. Besides, most of the small engines are not even available with electric start so your dilemma is solved.
Low-level fun/slalom addict:
You will need a powerfull motor and your paramotor will be heavy. So add the electric only if it is very hard to start the manual. I would say anything up to 200cc is OK to start manually. Larger motors would need electric.
Acro pilots tend to turn their engine off for their stunts. Even if they do not, sometimes the engines stops itself. Engines with no clutch rotate at idle. During SAT maneuver the pilot and paramotor actually fly backwards and backward airflow brakes the prop and may stall the engine. In such cases the pilot may need to restart the engine quickly. Having a button is handy.
For thermalling it does not really make a difference. Maybe electric would be better as after a long flight with motor off the engine cools down and is harder to start. But once fuel evaporates from your carburetor after long flight, you may not be able to restart the engine either. On the other hand, for thermalling a small engine is perfectly sufficient and these come with manual starters anyway so your dilemma is solved. These engines usually have choke so you could assemble a wire to operate it in flight and you could restart your engine easily even after longer periond.
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