This works great to verify that all wires are connected and working. It will show opens, mi-wired pins, and shorted pins or wires. It cannot test that the twisted pairs are mated to the correct pin pairs but this is a minor issue since that is easy to check visually. You can use 2 short jumpers to test your premise wiring.

Ordered on the Monoprice site along with some other items. Did not receive in the shipment, so ended up purchasing on Amazon. No way to make contact with Monoprice. Email form not responsive after 3 weeks, no chat available, and no phone service available as well. In all, a pretty miserable customer experience. Started a charge back for the mising item.
Other than that, the product works as advertised.

Simple device, but a great time saver when installing wired network. At only about $10 I should have bought one of these years ago.

I make up my own RJ12 straight-through and RJ45 crossover and straight-through cables for model railroading. This tester is simple but effective in this role. Verifies all conductors as continuous (or not) and that they are of the correct pin assignment (straight or crossover). You have to know what a crossover pin out should be, but a quick cheat-sheet and eventually your memory will be enough. For simple installations I can recommend this tester.

really easy to use. needs a 9v battery

Tester has been working great so far. No issues.

Makes building and testing your own cable runs a snap.

Got a lot of faults readings Not sure it was all testers problum

Great tool. My only gripe is the 9V battery. It would have been great if the batteries were AA or something a bit more common. Not that 9V batteries are uncommon, but I certainly have more AAs at home than 9V batteries.

Good tonner is work good