The adapted Swytch kit on my ancient tourer and the more recent Decathlon 500E are allowing me to continue enjoying some local cycling and light touring as I approach my eighties but they both suffer from increased weight and poorer handling. I had hopes for less conventional conversions such as from Revos, Alizetti, and Skarper but they all seemed to have fallen by the wayside. My cynical side suspects that major players don't want to overcome the undoubted problems associated with those 'solutions' - more money to be made in other directions? So it seems I will have to rely on the unlikely chance of acquiring a new body in the (distant?) future, to recover the sort of cycling I enjoyed in my earlier years.
The weight of a conversion shouldn't be a problem when riding, since the assistance of the motor overcomes the momentum and any additional resistance of the motor.
You can make a really nice lightweight conversion that doesn’t affect the bike's handling and gives a very nice assisted ride by using a Lightweight rear motor, a KT controller and a 10s2p battery from Aliexpress. The total additional mass is about 3.5 kg. You can often claim that back with a lighter crankset and pedals, a lightweight seat post and seat, carbon fibre handlebars, and lightweight rims, spokes and tyres. Tyres, seat and crankset give the biggest savings.
Swytch and the other front wheel kits are OK if all you want is a bit of extra assistance to get you up the hill to work, but they're pretty bad compared with rear motor kits with a KT controller.