It looks Dash is into budget e-bikes. I had a look at their selection.
Your needs are minimal as for an e-bike, although they might grow in time. The e-bike that really drew my attention was
Cowboy ST4.
- It is a low-step bike so given your height, you should not have issues with getting on or off.
- It is lightweight as for an e-bike, which is a real bonus in the big city of London.
- It offers pretty low power and the battery is smallish but that's the price for the e-bike light weight. Regarding the low power motor and small battery you said yourself you are not travelling for long distance and you only needed extra boost.
- The next thing about Cowboy ST is the carbon belt drive and single speed. No drivetrain maintenance needed but you would have no gears either, meaning more assistance and harder pedalling uphill. (Which should be not that complicated in London!)
Cowboy ST4 is a totally integrated e-bike. It means the repairs might be complicated unless Dash would ensure full technical support and warranty handling.
Another e-bike I liked was Volt Burlington. Heavier than the Cowboy ST4 but with a bigger battery, classical drivetrain (needs maintenance), and traditional bike components (should be easy to repair).
As I can see, you can book a demo ride. Will you? Ask about potential repairs and warranty!
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You want to lease an e-bike from Dash. Cowboy ST4 is £3,000.
Why wouldn't you talk with a Specialized dealer on either of these e-bikes?
https://www.specialized.com/gb/en/turbo-vado-sl-4-0-step-through-eq/p/188206?color=317862-188206 £2,900
https://www.specialized.com/gb/en/turbo-vado-sl-4-0-step-through/p/188205?color=303882-188205 £2,800
Perhaps Specialized can offer financing? The brand is big, these e-bikes are excellent, with very good service and the best warranty. Try talking with a big Specialized owned store in your area! (Ask for the size S!)