I had the 8017 and liked it. Never had any issues except for the 2 way remote having the battery tab break off when I replaced a battery. I did a lot of micro/macro soldering in the military so for me it was an easy fix, but for others most would have to resort to buying a new 2 way remote. Anyways, I started to have problems with the tilt sensor as it would start to give me false readings/chirps/alarms/etc...
I have since then upgraded and spent a little bit more money on the the Scorpio SR-i900R and definitely wish I would've done it from the get go. I am now looking at upgrading again to their rLink model that has GPS tracking (requires a monthly/yearly data service premium after the first year). I am on the fence on whether to do it or not and I don't think I will since I moved away from Tucson, and bike theft here in North Dakota isn't as big as an issue. But if it is in your area, you may want to invest in it. There is a reason the Gorilla is cheaper... you get what you pay for.
But definitely, if you can afford to upgrade, go ahead and do it. If not, then continue to use other layers of security on top of the Gorilla alarm and you'll be okay until you can upgrade. Which you should be doing anyways... Personally, I run my Scorpio alarm, lock the steering column, have a Xena 120db disc lock on the front rotor between the fork and caliper, another Xena 120db disc lock on the rear, a thick cable lock I string the rear wheel up through the swing arm and my Sato rear hooks, as well as an H-Base lock for my front wheel and another H-Base lock for my rear. Overkill? Yeah... but I sleep easy at night knowing someone is going to have to try to overcome 7 different security solutions on the bike alone, not mentioning breaking into my garage and not set off those alarms or set off both proximity sensors on my two way vehicle alarms where my bike is strategically parked in between.