This is kind of a "to each their own" type thing. I've flown many aircraft with different, or no, warning systems whatever. I prefer no warning system, and a diligent pilot. The challenge with differing warning systems is that there always seems to be either a combination of circumstances which defeat it anyway, or they simply quit working, and the pilot does not notice. Wrong warnings ingrain deliberate ignorance.
The one says it will state "test ok", and that's nice, but if it has quit working, and does not say anything, the pilot won't know it's quit, and then land gear up (or down) without the warning (presuming that they're not paying attention in the first place).
Airspeed sensing systems have to be very carefully set up, or the pilot can get repeat warnings, which are simply a nuisance. I muffed setting one up in a 182 amphibian, and asked that it be set to warn slowing through 80 KIAS. 80 KIAS sounds like a good speed for approach in a 182, but it's too good. You slow through 80 KIAS, and get a gear warning, you speed up to 82, and the system resets itself, so you get another warning when you slow through 80 again, and so forth. So during testing, I just pulled the breaker, and did my standard double verbal look, check and speak the position. Or, you get the bug in the pitot tube....
Radar type systems seem interesting, though some ground surfaces absorb some radar frequencies.
The Piper Arrow had a neat trick for a while, the gear would drop itself below a certain speed. It caused a kind of problem though if you wanted to get out short, as you'd have to lock this system out to get the gear up at a speed to allow a climb out at Vx. They were removed - by AD, I think.
Pilots defeat the type design warning systems - Noise cancelling headsets can cancel warning horns. Gear warning horns which are throttle position activated, are defeated by pilots who carry power into the flare. Flying the Navajo, I got in the habit, in addition to my look and say, of closing the throttles well back on final, to listen for a horn, and then sneaking in a little power again, to stretch that approach and flare into a greaser again.
Amphibians don't know where you're landing, so they tell you all kinds of things about the gear position, no matter how diligent you were in selecting it correctly. Just distracting, particularly when you're trying to tuck into a tight lake.
In my opinion, instead of buying gadget systems, pilots should rely on the one (if any) which was approved with the type design, and dedicate themselves to simply paying attention to the gear position by the most simple means. No false alarms, failed alarms, missed or unheard warnings, or expensive systems to buy and maintain. There are a lot of things available for planes and pilots, which, in my opinion, planes and pilots should not need....