IMHO, a hotshoe-mounted GPS logger is a useless gadget.
With the possible exception where the device includes a compass and records direction information as well. But the latter could be done (and written to exif) by the camera anyway w/o any need to receice GPS.
I geotag ALL my images.
I have a stellar GPS logger sitting in a pocket of my photo bag (I upgraded from SIRF-III to a
Wintec WBT-202 which never disappointed me and always knows precise position. Even within most buildings. It autoswitches off to save energy (it has a motion sensor to switch on) and can stay in my photobag for days until I synchronize my SD card with my computer. At the same time, I would plug and charge the logger (appears as an USB drive containing the track file) and exchange the cameras battery.
In order to actually geotag my images I use GeoSetter (on PC) or PhotoLinker (on Mac). Both update the image files exactly as the camera would do. It's as simple as "open image folder and track file and go". Then I import to LR. I'll have a blog article soon for anybody migrating his geotagging workflow from a PC to a Mac.
No way I would use a hot-show mounted logger: To clumsy (ugly to the point of ridiculous, easily breaks, doesn't fit my photo bag, blocks my flash) and unreliable (probably sub-par GPS receiver, probably misses fix when a photo is taken as it cannot always stay on) and can't be used to geotag photos (from a second camera I carry with me) and is incomplete (doesn't write the location names aka reverse geocoding). The iPhone geotags its images and try it: positions aren't reliable.
So, a hotshow GPS logger is a gadget for people who don't need the feature.