Sorry, I meant the GBU421. Got it initially as a cheap ($9 at the time holiday sale) experiment. I guess the DBT-120 would have been the second choice if the GBU421 hadn't worked. But it did so I never tried any others.
Note, I plug the dongle into the back of my 27" monitor so that it's within a 1'-2' of my mouse so there is no problems with the mouse. But with this dongle, and I assume any other (which is why I never tried any other), when I sleep my machine (I never shut down) the power goes off on the monitor and computer (which goes into a standby mode). This means no power on the dongle. So you cannot wake up your machine using with BT devices. I have a wired keyboard so I just hit a key on it to wake my machine up.
Another small "quirk" with the dongle. Maybe about 15% to 25% of the time the mouse will not immediately re-pair. Trackpad almost always does. So when that happens I need to flip the mouse power switch to "get the machine's attention". Then it re-pair shortly after. I've just learned to live with this "quirk". I assume other dongles may behave the same under these conditions. Interesting enough, the re-pair is immediate when rebooting.