So I own a DSO Quad and I like it for a lot of the OSSC work.
One problem – HDMI – it is VERY high bandwidth and speed. Testing HDMI signals properly usually requires GHz oscilloscopes and test equipment can run literally into the hundreds of thousands of dollars. Software installed on these kinds of oscilloscopes costs thousands to do HDMI compatibility testing. You do not NEED this but In the event you need to test the HDMI signals beyond basic connectivity tests.
A TMDS pair signal sends about around 2.7-3v on each line so you can test those with a multimeter.
The DSO quad works up to 8Khz and can test most basic signals (for instance I can easily
test HSync, Clock and VSync on my OSSC).
For true HDMI or DVI (anything TMDS) debugging you need some serious equipment – if you are lucky you will never need this but I got I to some trouble with my OSSC with HDMI and a basic oscilloscope won’t realy help you here (at least with the knowledge I have!)