Garmin Black Boxe Sounder Models - GSD21 vs GSD22?

[nickfishbait]

I am looking to buy a black box sounder for my 3205c with an airmar P79 transducer. Does anyone have experience with either the GSD-21 or GSD-22 units?
The BIG difference between the two (besides double the price) is the 21 is analog and the 22 is digital. Is there a big enough difference in picture quality to make the jump to the GSD-22?

Thanks,
Any help is appreciated!

Nick

[catfish hunter]

I have the gs 22 and it works nice,I have about 22 trips w/ it and I like better than any other one I had in the past,I use it w/ the 4208 unit