I bought 2 of these to try for a local drama group, in the past we've used overhead microphones but have had issues with feedback and clarity. They're also a pain to setup involving stepladders.
These boundary mics were bought as a test and they are impressive! The clarity is outstanding, a good natural sound. They're a doddle to set up and invisible to the audience. A pair of these at the front of the stage picks up the entire cast far better than overheads do - I'd advise being pedantic and measuring the distance that they're set up (I put the an equal distance from each other and the edge of the stage). We also have the bonus of being able to use them on pretty much any stage we use, there's no concern for fixtures or mounts.
As these as boundary mics they work less well on carpet and some EQ will be needed as footsteps do get amplified a fair bit.
For any amateur theatre group I can't recommend these enough. They're insanely cheap, the sound quality is great and most importantly they are rugged - you really don't need to worry if they get kicked by accident.