You could just open it up, to see what parts are used. Or apply known signals and see what the approximate bandwidth could be. Its quite old, no-one might have scanned any user manuals or datasheets online. It might have sold in very low volume at that high price but I'm speculating. You might have the 255th one ever sold if they started serial numbers at 810000.
Does it have a BNC socket? I can't see one. In any case, you could connect this device up to any audio source (e.g. PC headphone output) and generate a tone, to see if it works to 20kHz. Or use a 555 chip and see if it works to a few hundred kHz. There are plenty of ways to find our for yourself what the bandwidth is.
I only watched the last 2 minutes of it, it doesn't seem great (and the 1C15 looks worse),
However, both of them will likely be a lot better than the 707, but that's an extremely low bar (single channel 100 kHz is of very limited use).
What's your use-case and your budget? A decent 'scope will be closer to 150 euro. However if all you care about is approximately seeing the presence/absence of a signal with no significant accuracy or reliable triggering, then you could just about get any cheap 'scope such as the ones you indicate, and it will be better than the 707 as mentioned.
