Anyone been there? Does it make a good day out (how long to see it all)?
I visited Milestones about four years ago, so this report may be out of date here and there. However:-
Milestones is a good museum relating to transport and everyday life in the past. Although housed in a modern hanger-style building, there are several "street scenes", mock shop fronts and workshops, giving the place rather a film-set feel. Some of the vehicles are excellent, and they are well and accessibly displayed. (The Portsmouth tramcar is unusual in being an example of a horse tram rebuilt and converted to electric traction.)
This is, however, an essentially static museum. I don't know how much (if any) interactive interpretation takes place - I don't recall any from my visit a few years back. But there was probably a video or two to see.
Several of the sets have quite a lot of detail in them, and if that's what you like then it could take quite a long time to see it all. If not, you could whizz round quite quickly. The website recommends you allow 2 to 4 hours - I'd have thought 2 hours (plus the coffee shop and gift shop if required) would be enough for most visitors.
The "Centre Shuttle" bus links Milestones to the railway station, running every 10-15 minutes. If interested, check whether this has been a victim of cuts since I was there!