Reg, thanks for the insights. The ZT-702S (scope + DMM combo from Zotek) has a lot of aliasing past 5MHz (its specs are up to 10MHz), but at least it gives accurate measurements and waveforms up until that frequency. In comparison, it seems a more finished product: no screen blanking and no edge rolloff.
In practice I have seen myself carrying the ZT-702S more often than a plain meter when I have to do equipment diagnostics in the field - at least I can get a waveform from the various power rails and detect if capacitors are starting to go down, not to mention an easy way to trace audio or otherwise slow signals. Debugging any serial communications protocol is entirely out of the question, but there are other instruments for that.