Beginner’s knockblock buying help!

Good day to all of you in the community! I whould like to ask from your experience which knockblock whould be the best choice for someone who is starting in tuning industry! Plex equipment is a renowned here in Greece but is a bit expensive for someone that is starting right now! I now of the phormula product and the G4+ knockblock and the knockbox product! Also through my search online i’ve seen some DIY knock detection amplifiers. Does it worth it to go the DIY way? Are they reliable? Should I spend money on a fairly priced knockblock or it whould better to go directly to the top shelf products? For starters the use i’m Going to do is tune my own cars + some friends and maybe later going pro!

I know a lot of tuners who use the old tech det cans, as described here:

http://www.enginebasics.com/EFI%20Tuning/Det%20Cans.html

There's also the computer based Tuner Tools Knock Monitor:

https://gumroad.com/l/tunerknockmonitor

Personally I'm using Phormula KS4 pro kit with a Link G4 Knock Block for the audio