I am assuming that the Ifinder is the more expensive of the two after viewing the specs on these two units.
My opinion is: Yes, the $50 is justifiable for the higher unit.
-The Ifinder has a 1.7 x 2.2 display screen. The Globalmap 100 has a 1.5 x 2.2. Larger display goes to the Ifinder.
-The Ifinder has 120 x 160 pixels. The Globalmap 100 has 160 x 104 pixels. This is confusing, but I'd say that the Ifinder has a clear advantage here.
-Both units have excellent visibility in direct sunlight.
-The Ifinder has 1000 waypoints while the Globalmap 100 has only 750 waypoints. I can't see you marking 1000 brushpiles, but you never know...
-The Ifinder has 10 savable plot trails whiel the Globalmap 100 has only 3 savable plot trails. This comes in very handy and is almost single handedly worth the $50. If I can plot and save 10 versus only 3 trails, I am definately going with 10.
-The Ifinder has a map zoom of 0.05-4000 miles and the Globalmap 100 has a map zoom of 0.10-2000 miles. Seems that the Ifinder could possibly get you twice as close to your target.
To me, it is well worth teh $50 more. I don't use Lowrance, though. I use a Garmin GPSmap76..... For what you are wanting, these Lowrances will do just fine.
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It's only fishing.....