Small screen and low power, most of the low cost units are very poorly made. Sail has the Helix 5 for $250 which is the best value sonar out right now in my opinion, you will be kicking yourself if you buy something like a Humminbird Piranha or that Hook unit.
I can't speak for the helix 5 or the Hook, however i was recently given a pmax 197c by my father who replaced it with the helix 5 di (which i will hopefully get to see in action soon) and paired up with the ice ducer, it's really a great compact unit to have with you on the ice if that's what your limited to. The colours help identify size and density of objects beneath you with almost real time accuracy. I can easily read a micro jig which i never thought possible with a cheaper unit, and as far as power goes, i leave it on from almost the second i get on the ice to when i get off (6-10 hours) and yet every time i plug my battery in to charge, it says fully charged within 15 minutes and has yet to give up on me due to cold weather. The small screen is an unfortuante truth, but in a hut you really don't need a whole lot bigger. Obviously with the sale price of the helix 5 you wouldn't be considering a pmax, but anyone wanting a sonar on a budget should at least go look at it