I have a red one looking for a new home, if you want to try it - just the cover (I sold the bag).
I like them and have had them for about 20 years, but I like the BMW tank bag even more.
Here's a few pros & cons, from my experience.
The most important ones first:
- Bagster isn't waterpoof unless you put the (supplied) cover over it = a fiddle in the wet. It's still pretty good without, i.e. it has to be proper rain for 20-30+ mins to get through. The BMW bag is properly waterproof - it doesn't leak (sealed zips & inner drawstring waterproof liner). Big plus for the BMW.
- Bagster gives good tank protection (inc knees), the BMW bag will leave marks after a few years of use. However, you can get some scratching of the filler cap from a Bagster since it has a hole cut in it for filling, and the bag touches it. Bagster wins, just.
- BMW zips are only good for around 5 years* regular/heavy use (30k miles say) - then they start to fail. Bagster zips are sturdier, probably because they're not the fancy waterproof ones. Bagster wins.
- Bagster has more choice of sizes, and is slightly bigger than the BMW bag - squarer - which helps if you're carrying a laptop, etc. Bagster just wins.
- BMW is tidier design & clips, IMHO. There's something very 70s about Bagster leatherette.
BMW wins.
- Both extend, if the you get the right models. It's worth going for the extending versions, either way. However, the BMW one is getting rare/expensive.
*The two BMW bags I've worn out have both been secondhand, so I can't guarantee the lifetime. But I have an actual new never-used US imported one lined up for this year's touring. I'll tell you how I get on in about 30k miles...
EDIT: I should have said - this is for the K1300S BMW tank bag (20 litres expanded), not the older K1200 tank bag. I'm pretty sure both fit a K1200 though.