Looking for a good knock detection system

Hi guys, I'm in the market to buy quality knock detection. I've looked at the plex knock block, haltech knock ears, and the phormula ks-4. As much as I would like the plex knock block it is just too far out of my price range. The haltech knock ears is in my price range as is the ks-4. My budget is right around $700USD. If you guys have had experience with either of those or have recommendations for others. Any help is greatly appreciated.

I've used the new Link G4+ Knock Block and would highly recommend that. It should also leave you a chunk of change given your budget. I particularly like the onboard battery that's rechargeable via USB. I've tested it on a range of cars and found it to be very effective.

I use the Phormula KS4 kit (5years) and love it and has not let me down.

I have the phormula pro kit, love it.