I've purchased four zapper rackets from Amazon so far:Elucto 2-wire / 2xAA battery / 3200~3500 voltsBlack Flag 3-layer / 2xAA battery / 2750 voltsLanpuly 3-layer / USB rechargeable lithium-ion battery / 4000 voltsZapIt ! 3-layer / USB rechargeable lithium-ion battery / 4000 voltsThe Rechargeable Zap It! is by far the best, due to the grid design and higher voltage. Here's what I've learned so far:3-layer is better than 2-wireExamples of 2-wire, single-layer designs include Executioner and Elucto. To be zapped, the bug must touch 2 wires. It works well for larger bugs but in my experience, small gnats pass right between the wires with no effect.The more common 3-layer design has an inner "hot" grid separated from the outer "ground" layers with plastic spacers. To be zapped, part of the bug has to go far enough in the mesh to touch the center grid. You'd think it would be less effective… but in my testing, it works equally well on large bugs … and much better on small flying gnats.USB rechargeable lithium-ion battery is better than AA batteryZapper rackets are usually powered by two AA batteries or a single USB rechargeable lithium ion battery. AA battery powered zappers are rated between 2750 & 3500 volts while USB rechargeables can go as high as 4000 volts. It’s a difference you can see and hear … and the higher voltage improves the chances of a kill.ZapIt ! USB Rechargeable is the best I've triedOne way to test a zapper racket is to press it against the foliage of a plant with small leaves. It shows how sensitive it is (how many sparks) and how powerful it is (how loud are the cracking sounds)Lanpuly was the first 4000 volt, USB-rechargeable racket I purchased. Doing the foliage test, it didn't work nearly as well as the Rechargeable ZapIt!The voltage is the same so what's different? It turns out the internal gaps between the 3 layers in the Lanpuly are wider … so bugs are less likely to touch the center layer. The ZapIt! grid spacing is closer and in the foliage test, it produces far more and louder sparks.For use on bugs, it's also the best I've tried. As an example of the power and sensitivity, I placed the face of the Rechargeable ZapIt! on a silverfish on the carpet. The result was a loud display of sparks like the 4th of July ! The silverfish was vaporized … and the snapping, crackling sounds were so loud that they startled my wife in the next room !There are three sizes: Mini 16" long x 6.3" wide / Medium 18" long x 7.6" wide / Large 19" long x 8.3" wide. I've tried the Medium and Large and recommend the Medium as the slimmer grip makes it easier to snap your wrist back and forth while also having to hold the power button down with your thumb. There's no reason to get the Mini in my opinion.Note: Amazon also sells ZapIt! rackets powered by 2xAA batteries that are only rated for 3500 volts. Unless USB charging is not available, that option is not recommended.Tip: an iPad USB charger charges faster than a smaller iPhone "cube" chargerI hope this information is helpful !