I have both the Tom Bihn TriStar and Western Flyer, Eagle Creek Adv Weekender and have looked at the EC convertabrief (saw it in the wild once).

For just carrying a laptop, gear and papers, I think of them as too big unless you have a lot of stuff. With the WF, TS and AW, you would also need a sleeve or something similar as they have no real padding or support to them for a laptop. The EC Convertabrief is similar in size to the WF and has a dedicated laptop area so it may be better than than WF though they are similar in size.

I think of most of these bags as "one bag" for trips as they are large enough for your gear and a night or two worth of clothes while not being too big or casual to take into a professional setting. Basically they are middle ground between luggage and a laptop bag IMHO.

As for searching for similar bags, they generally go by the term convertibles or something similar.