bigclive works on electric / electronic stuff, and he's sometimes a bit sniffy about cheap hobbyist kit. (Fair enough when he's talking about things you use with / on mains electricity where there's a risk of death.)
For RS232 any 'scope is going to be fine, even a chinese clone knockoff or an ancient second hand scope.
For decoding serial one of those $5 logic analyzers is more than sufficient, you don't really need an oscilloscope at all. I don't really like using protocol decoding on my scope unless I need to correlate timing with an analog signal because it's tedious to set up and use for a simple digital signal.
RS232 is 12V, but a couple of resistors would sort that out.
If you're a beginner I would actually recommend the Saleae Logic Analyser over this scope, unless your routinely dealing with analog or voltages over 5.5V, the Saleae is much more useful, has serial (and other) decoders built in as opposed to having to pay extra on the Rigol, has better capture and triggers plus as a bonus it doesnt have that noisy fan going all the time.
Yeah, in the article he uses a good old MAX3232, which is specifically for doing RS232 to TTL level shifting. Totally agree, the Saleae or one of the cheaper clones I linked is a better choice for most hobbyists. Scopes are indispensable for certain uses, but most Arduino/RasPi projects these days are all digital and you can do everything you need with a logic analyzer + a decent multimeter.
I use my scope just often enough that I'm glad I have it, but I sometimes also regret buying it because it's not that often that I actually need it.
While cheap knockoff analyzers often ship with pirated software (e.g. Saleae) many, if not most, work equally as well with the open source Sigrok software.
Saleae gives their software away for free, there's not any need to pirate it but still using their software is morally shady IMO because they put a lot of effort into it. I prefer Sigrok anyway, even with the actual Saleae analyzers.
Also worth noting that Sigrok loads the analyzer with open source firmware, you're not using any pirated code. The hardware is basically a clone of the original Saleae logic analyzer, but the Saleae hardware is just a standard reference implementation of a cheap Cypress chip so that doesn't really bother me.
For RS232 any 'scope is going to be fine, even a chinese clone knockoff or an ancient second hand scope.