I had a shark 2500 for about 6 or so months i think running .5 ohm with stock alt and a 1 extra battery. Did well for me for the price(i got mine for $100). Never protected or got to hot that i can recall. Did a 145.8 Sealed on the dash(legal) with 1 Dc Xl-18 M1 in my previous hyundai santa fe with stock alt, and 1 extra battery.
I say its a good amp for the $100 mark. but wouldnt buy at the current going price.
No as for the shark 3500, at the $300 price i wouldnt buy it. I would get one of my Soundstream Ta1.3ks before i paid 300 for the shark. Just my personal opinion. I think my Ta3k will make more power then that will and is more efficient.