I do agree it's not convenient (as you need to swap probes and do another reading if you want both MISO and MOSI) but it can do it.
The entire reason for my buying a DS1054Z was to use CS' on a channel to trigger and the other 3 channels to decode an entire transaction, MOSI, MISO and Clock all on the same screen. It was the driving force since I already had a two channel 350 MHz Tek 485.
Since, I have decided that the Single shot capture is a more important feature but it wasn't apparent when I made the decision to buy the Rigol.
If I were buying a new digital scope, I wouldn't consider anything that didn't have 4 channels.
I don't use 4 channels very often but if I didn't have them I couldn't use them at all!
There are two entry level scopes that come up all the time. First, the older (more mature) Rigol DS1054Z and the newer Siglent SDS1104X-E. I would give the nod to the Siglent because a) it purportedly has a more responsive user interface and b) it can be unlocked to 200 MHz and more bandwidth is good.
Before I settled on the Siglent, I would want to wander through the Test Equipment forum and review any open firmware issues. It took Rigol several iterations to finally get it right and the Siglent is a lot newer to the market. I haven't followed along so I don't know where this stands.
Not every firmware issue is a show-stopper. If it is for an edge case where I'll never work, who cares?