I certainly wouldn't call it robust. I have had 2 GSC10s break within a year. Same problem: reed switch in speed arm starts working intermittently and eventually fails altogether. Plenty of other reports from other dissatisfied users. The Motorola/Bontrager sensor has the advantage that you can move it easily between bikes because it doesn't attach with cable ties (the
Decathlon one is also relatively easy to move). The Decathlon one also comes with a neodynium magnet for the pedal spindle which is a much neater solution for the cadence sensor.
Like I said, my unit has been very robust, the battery lasted 3+ years, ridden about 800 miles a month, in all weathers, cleaned by placing the bike in the bath (with the wheels removed) and spraying a shower over the whole thing including the sensor, involved in numerous "incidents", took a good clouting from the wheel magnet a few times. Never missed a beat. Maybe I am one of the lucky ones, but based on my experience, I can't fault it.
Consider the volume of units sold vs those sold by other brands and then consider the relative number of complaints per unit sold. I would guess that they don't come out looking so bad when you take the number sold into account.
And if it does go wrong, Garmin aftersales is very good.