I'd allow the goggles but give the "fragility" a mechanical definition. This makes sense in-universe, without being too good.
Whenever the character takes falling damage, crushing damage (like from an avalanche or rock trap), or a critical hit, he has to make a Dex save (DC = half damage taken) or the goggles break.
Or you could make a "breakage check" for the goggles after every encounter. Roll a d20. On a 1, they broke. If it was a really rough encounter maybe increase the DC to 5 or 10.
Or you could have the character make a "maintenance check" with every long rest. On a failure, the goggles are loose and next time the character takes damage, they break. This way you only have to worry about it occasionally.
You could give the character a temporary Flaw: fragile goggles. Then when he needs Inspiration, his goggles break. (The FATE solution.)
Either way, at 100 gp a pop the price of goggles could add up fast.
Whenever the character takes falling damage, crushing damage (like from an avalanche or rock trap), or a critical hit, he has to make a Dex save (DC = half damage taken) or the goggles break.
Or you could make a "breakage check" for the goggles after every encounter. Roll a d20. On a 1, they broke. If it was a really rough encounter maybe increase the DC to 5 or 10.
Or you could have the character make a "maintenance check" with every long rest. On a failure, the goggles are loose and next time the character takes damage, they break. This way you only have to worry about it occasionally.
You could give the character a temporary Flaw: fragile goggles. Then when he needs Inspiration, his goggles break. (The FATE solution.)
Either way, at 100 gp a pop the price of goggles could add up fast.