I'd built a little t-bar out of old pop-up shack poles to hold the boat transducer down the hole, and it worked fine.
I picked up an ice 'ducer for my Striker 4 last winter and am happy I did. It's just easier to get it pointing straight down.
It's heavier duty and rubberized, too. Just a feeling, but it seems like the cone is more true with the ice 'ducer as well.
It's better, IMO, but isn't essential.