Depending on how much you want to ride your Vaya but could do with some help, you might consider a Keyde S110 hub motor. Weight 2.3kg plus a 1.2kg 36v 7ah battery is same as published wt of Mahle x35 system comes in thru axle and threaded axle versions. As easy to install as changing a rear wheel. wireless controls or just use your cell phone and app. Only one wire to battery. I've ridden mine on routes with several miles of near continuous climbs with up to over 12% gradients. Given the right expectations I think it is a great system.