Yes, knockoffs of Denso are crap, but Denso is a primary manufacturer of automotive sensors, electronics, solenoids, etc (They are a primary supplier for Honda and Toyota). If you can find a genuine Denso product on Amazon, Id say go for it. I've bought 2 Denso O2 sensors and a Camshaft Position Sensor all off Amazon and they came in genuine Denso boxes, and were roughly $50 less than genuine Toyota products. None have failed since installation and its been a few years for the CPS and roughly 2 years for one of the O2's.
If the product comes and it looks/feels cheap, or doesn't have the Denso branding, send it back.
Hope this helps.