Matt,
I can only answer your question obliquely, but it might still prove useful:
I chose against a cycling-specific GPS and instead went with a Garmin 600T, generally regarded as a hiking compass. Filled with open-source maps (like those from OpenStreetMaps), it is a nice complement to my GPS-equipped smartphone, also filled with open-source maps. I will sometimes download maps to my phone, then transfer them to the GPS by updating the micro-SD card in my OTG smartphone reader/dock. In this way, I don't need a computer for the task.
I chose a hiking GPS because so much my cycling time here in the States is spent off-road, cross-country, or on Forest Service and Bureau of Land Management lands. It still works fine on roads. This GPS' predecessor, a 400T, gave good service on my double crossing of Europe last summer, but failed on my return through Romania the second of three times when the plastic switch cover herniated and split, rendering the unit no longer waterproof and inoperable except when prodded by a sharp stick. The 400T is considered obsolete by Garmin (their products seem to have an effective support and service life of no more than five years) and no parts or repairs are available. The button cover is molded as part of the case upper half, and only available as a salvaged item from a same-age unit, so any replacements are unlikely to be in good shape now. I can effect a workable fix myself, but it could be unreliable in an emergency, so that unit is now retired, replaced by the 600T which I use for hiking and all back-country adventures. It has the same basic design, so I expect it to also die similarly after exposure to playa sun and alkali.
The 600T will also work with an available Ant+ cadence sensor if desired. The sliding rail mount works nicely on handlebar, stem, or top tube. I do get an honest 16 hours' use on Eneloop XX batteries, which I recharge using my TTTP2+ and SON28 dynohub with an Eneloop AA/AAA charger. I can also power it directly, sometimes with the lights running, depending on my speed.
Materials degradation is something to keep in mind with all GPS units by pretty much all makers. Use and weather exposure (particularly to UV) can eventually kill them in simple but fatal ways, so it is best to consider them an interim rather than permanent purchase, even if the maker promises free map updates for life. Often, that can mean only for the effective life of the product (doesn't matter to me, as I use the open source ones and Russian ones, as mickeg does).
All the best,
Dan.