Probably a bit early for reviews on the 400 as they've only just come out
Personally I have the Rider 5, it's expensive I must admit but you do get free map updates for the life of the unit so that is something to factor in
It's very simple and intuitive to use and the lane indication is great, it's really a general public (no brainer) satnav, you can also use the included Tyre software for route planning if you can be arsed to learn how to use it
Mine works well with a Sena bluetooth helmet intercom and the touch screen works well with normal leather gloves
The base supplies power if you want or the battery will last all day
It works fine inside a car but if you do this often you'd really need the TomTom accessory base with a sucker mount and built in speaker as there is no speaker in the unit
Maybe the Garmin is little more technical if you go off road etc, maybe a bit more hardcore ?
I'm very satisfied with the TomTom mounted on an Engimoto bracket