Link above showing up as 'no longer available' for me but found it on Swytch page. Generally they seem to be priced a little high at the 'special offer' prices and absurdly high at the nominal 'full' price. For range, where 'up to' ranges are quoted I use a rule of thumb: 1/3 of quoted range for actual useful range in more typical conditions.
Actually I found the capacities and they aren't as bad as I had guessed. Putting some reasonable settings in the Bosch range assistant and allowing for battery size the 50km kit might give not too far off 40km, and could almost certainly be coaxed into giving more then 50km in ideal conditions.
www.swytchbike.com
[35Km kit]
36V 5Ah = 180Wh
Expected range 35Km at 125W average power output. 10-15 miles at constant maximum power 250W.
50 Km kit
36V 7Ah = 250Wh
Expected range 50 Km at 125W average power output. 20-25 miles at constant maximum power 250W.