I would consider that a risk, see Fi’s track record of honoring promotions/discounts.
There forums are full of users who have never received the discount for past promotions or refunds…and many folks who have had an extremely difficult time even contacting Fi support.
I would read the terms page which u can find after a couple clicks on their sale page…
But the deice must be bought from Fi Store (NOT Google Store …this is an important point) AND must be activated on the same Fi account purchased under within 30 days starting the day the device ships. If not activated, they charge your card the full price.
But again, I see many folks who have been down this road and end up being charged by Fi regardless, or being told they do not qualify for the discount when in fact they do.
Just saying, I don’t trust Fi…and have had the personal experience to back it up. Your millage may vary, but at least be cautioned about them.