I had a 334 (older version of what became a HDS 5) that I used on ice for years, sold it with the boat and now have an LX-7.
Lowrance:
Pros: Easy to use, GPS, ice pack fits in a bucket, easy to use on boat in summer
Cons: Target separation is 2 inches, so things can get a bit blobby, interference rejection
LX-7:
Pros: Great target separation, great battery life, great screen
Cons: interface is clunky, big and heavy, not compatible with MinnKota Universal Sonar
Both are great ice units. Overall, if the Lowrance had better target separation and IR rejection I would take that over the Marcum in a heartbeat.
The Marcum is a specialized ice machine with the nice transducer, IR rejection and .25″ target separation. You can tell that Marcum is new to the whole user interface/experience thing as it is a clunky machine to operate and there are some really weird design choices that were made that make it confusing to use (if you have the vertical zoom and depth, the scale doesnt line up etc).
let me know if you have other questions.