I too have been down the road of buying the not so useful items and then regretting it..Unfortunately that's another gadget I've already bought (I purchased the Garmin Virb for £74.99 as it's such a good price). But I really like the look of that one (which you recommended). Note to self: Ask on here before buying any more electric bike items!
Last night I had the fun of trying to find a bottle cage and a saddle bag. The Topeak Mondopack Hydro Saddle Bag seemed perfect - but turned out it won't fit on the saddle of my Cube (Reaction HPA Race 29) - yet ANOTHER purchase fail! So I bought a Cube saddle bag and a handle bar bottle mount (which will not doubt drive me mad)
After a few tries at saddlebags I decided to bin the cheap aldi and halfords bags and went to a bike shop to get a rack that would fit correctly and bought These.. The saddle bags were a bit pricey but well worth the money and fit securely to the rack and have Ample room for the odd top up shopping trip in one side and the winter waterproofs stay in the other. The central Black top bag carries my spare battery for longer runs, again amply supported by the rack, and the front frame mounted phone /storage bag has a clear slip in section for the phone and underneath is a compartment for all the batteries and other stuff that need easy access, including any charging cables which are easy to access.
http://www.ebay.co.uk/itm/ROSWHEEL-CYCLE-BIKE-BICYCLE-FRONT-TUBE-FRAME-POUCH-BAG-MOBILE-PHONE-HOLDER-CASE-/201166921700?var=&hash=item2ed67b9fe4
The Rack also has a dedicated rear light mount so that is also now safe, secure and right where it needs to be.
It all makes the bike heavy but its only weight and after all we have help ..
The only thing I struggle with is a bottle mount..... So far it goes in the rack bags.
Most of this was bought on other members recommendations so I agree its best to ask first, or buy twice!!