Yes, it’s cheaper than an e-bike, but at what overall cost? While this heading is more ... I’d recommend the Swytch Go, which is IPX6 rated. How long is your commute? According to Moovit ...

It adds around 4kg to the weight of your bike. The big rivals here are Swytch and Cytronex. The latter is a better system but it's also a lot more expensive, starting at around £883, while the £ ...