I have 4 rigs now and would like to put all four screens on one.  I'm not talking about a KVM where I switch between full screens on each, I want to be able to see all 4 screens in a matrix.

Found one of these on Amazon:
https://www.amazon.com/J-Tech-Digital-Multi-Viewer-different-JTECH-MV41/dp/B078KJY78J/ref=sr_1_12?ie=UTF8&qid=1517352289&sr=8-12&keywords=J-Tech+Digital+HDMI+4x1+1080P

It's only $139 and seems like it might do the job, but I haven't ever used anything like this or am familiar with these products.  Have used plenty of KVMs.

Oh, and for mouse and keyboard I already have Synergy
https://symless.com/synergy

That will let me use one mouse and keyboard and roll it across all 4 screens on the 4x4 matrix on a single monitor.

Is that HDMI multi-viewer a good one or is there a better unit or idea??