I believe the surest way to know is take your Garmin transducer with you to your Hobie dealer and check it against the Lowrance and Humminbird adapters.
You will immediately know if the size and fit will allow use in your kayak.
I haven't bought the Garmin yet - probably will though regardless. The wife's Revo 11 is needing a FF too. I removed the cover plate on my Revo 13 to take with me to help with a sizing guess for other transducers. I can fab up a mount of some sort, I'm just concerned the smallish hollow for the transducer was designed with a proprietary emphasis to Lowrance and won't allow just any transducer in there. I was hoping somebody had some been there done that experience - I hate to pass up the transducer ready mounting area.