Correct, the seat belt is not locked into the buckle, as the tension is applied by the attachment part and tensions against the bottom section of the belt which is a fixed position rather than against the upper part which runs through the reel
There might be an Isofix version, but not right now, but it wouldn't be really adding much ease of use as its already really simple to use
Yes they do fit onto pushchairs, well the Britax Visio, or the Vigour 3+ or the Vigour 4+, more models coming soon, and not just from Britax, were working with a number of other companies to get this to fit so that this option is available to more people
