Choosing a Geiger Counter: Cheap Beta & Gamma Radiation Meters (CAJOE, Smartphone Sensor)

I know it's not workshop equipment. But maybe some of you were playing with such equipment. Well, I am looking for a simple and cheap Beta and Gamma radiation meter. No madness, I just want to check the background radiation. Possibly see something more on a trip to Chernobyl.

I saw toys up to, say, PLN 300 on the Allegro. From a sensor connected to a smartphone, to simple, self-made inventions but described, for example, "original from the renowned CAJOE brand".

Has anyone used such a cheap invention and can comment on the accuracy / calibration of such low-end devices?

I have a Chinese KB6011 on a M4011 glass tube and can recommend it. It slightly lowers the indications due to the tube used, but it has a lot of possibilities for cheap equipment.
Smart Geiger in the PRO version is also quite ok and does not cause problems like the previous version. Pretty reliable indications.
Soeks 112 can be purchased for PLN 399 and uses a sensitive SBM-20 tube.
You can take a look at the Dosimetry blog - lots of hardware descriptions.