6 months ago I got this speed radar from Japan ( www.fromjapan.co.jp ) for about 130€ shipping and customs + taxes included. You can get it from E-bay nowadays as well. Everything is in Japanese but it's pretty straightforward.

There's only 4 buttons: the red one is the on/off, the 2 with the arrows printed on them are up and down and the 4th one is mode selection.

Turn the device on, select the club you're playing (Wood 1,3,5,7 - Utility 3 to 6, Iron 3 to 9, Pw, Gw, Sw, Lw or putter) with the up/down buttons put the device behind the ball at about 1.5m distance and go for it.

On the display from top to bottom you have:

the number of shots that were recorded in your training session
the measured club head speed in m/s (multiply by 2.25 for Mph)
the measured ball speed in m/s
an estimate of total distance (carry and roll) in yards
-smash factor

And if you have a smash factor larger then 1.4 a black circle lights up next to it with some japanese symbols that according to Google are pronounced "gooda shotta".

Pressing the mode button gives you the club averages of each club played, and pressing it twice gives you shot by shot information. The last 200 shots are kept in memory. You can clear the memory by pressing the down and mode button simultaneously.

The club head speed corresponds well to what I know it to be with my driver, but I did notice that the device gives me rather short calculated distances (especially since the manual states it is carry + roll); about 10% short. So I when I ignore it's says 'yards' on the display and pretend it's meters it's quit on the money. Anyway you can fine-tune the calculated distance of each club from 50% to 150% of the factory default. The lofts that are used for those calculations are in the manual; since I play rather conventional lofts I had to shorten the setting to about 95% for my short and mid irons, going up gradually to 100% for my long irons and 102% for my fairways and driver to get it right.

Getting into this setup mode : push the up and down button simultaneously and turn the device on (so that 3 buttons to press at once). Select the club with up/down and press the mode button to change the percentile of that club. Reset to factory defaults (all clubs at 100%) is done by turning the device on while pressing the mode button.

You can also use the device without a ball; it only displays club head speed and does not store the shot in memory.

When the device is put on a little tripod it works better then when it is placed on the ground. I designed a 3D printer bracket to be used with this little tripod: https://www.aliexpress.com/item/32579050544.html. And got a hard shell that just fits the unit : https://www.aliexpress.com/item/1005002566176901.html.

3D printer file + Google translated manual : https://www.thingiverse.com/thing:5347045