The AD2 was referred to previously: it is a toy with no proper connectivity. Electrically it has merit, but only 30MHz bandwidth and 14-bit. Were I going to get a USB scope and deal with its latency issues I would get the Picoscope 16-bit unit, which also has limited bandwidth and is a lot more expensive but is aimed more at audio work.
Alternatively, there is Dr.Jordan-MLS and similar that use 24-bit sound cards, but then you have uncalibrated inputs and outputs to deal with and the silly 3mm jacks to adapt to.
The stand-alone DSO as it is today seems to have a very quick probe-to-display time, which used to be much worse and was one of the things that kept me from going with a DSO when my first CRO died and I replaced it with an inferior CRO still in production last year. That one died at 18-months of age and will be fixed once the OWON arrives and I get it working for me.
Whether you have or get a USB scope, a DSO, or a used scope of any kind, it will be a novelty and allow you to explore and do new things. So of course it is great! If you get serious about whatever you are doing, then you will move towards the "real deal" for whatever that niche demands. For example, the digital channels on all these USB scopes and DSOs seem to only be able to handle TTL voltages at best, and some are only 3V or so. That is actually fine if all you look at is recent production digital. I'm old school and use CMOS at 9-15V in hard-ware-only circuits when I need something "digital". Even though the chips are capable of high speed, my applications are distinctly ultra-low speed inasmuch as they are logic for channel selection, on/off muting and similar things in audio equipment. So, the digital inputs on modern scopes are useless for what I do.
I'm not an RF guy, nor do I have a complete handle on all the DSO specs, but I believe that for those very high bandwidth apps, like GHz+ scopes, the low-bit converters are the only ones fast enough to do a capture AND the sample rate must be extremely high AND the memory depth must be higher than for a mere 1-200Mhz scope. All of that costs money. Lucky for me I don't need such a thing since I don't have that kind of budget.