I bought a vexlar FL-8 in 1993 and it's still working today, and it's been used a lot! I finally broke down and bought a new FL8 two years ago because my old one was getting hard to see when I was out of the shelter on a sunny day. It also didn't have the transducer on a float, it was on an adjustable arm. Most of my ice fishing is in shallow water, 20 foot or less, and mostly for bluegills and crappies. Though the FL8 is a very basic unit it works fine for my style of fishing. If you like fishing for perch or walleye in deeper water you may want to look for a unit that has the bottom zoom capabilities, and if you plan on jigging for lake trout definitely make sure the depth range is deep enough. The one down side to the vexlars like the Fl8 is if you fish without a shelter, snow does build up in the trough on the screen.
One word of warning though about getting a flasher/sonar for ice fishing- once you start using one you will NOT be able to ice fish without one. If my battery goes dead I'm done for the day now.