i have one pretty close to that, and it is doing my system quite will. a 1/5 HP is a bit low, but may still be fine. drop in chillers are easier to plumb than the in lines. $300 is a good deal if it is fully charged and ready to go. you will want to make sure that chiller is fully charged with refrigerant. it is not expensive to replace, but annoying.
I do not know if this help. I live in central florida and keep my house at 77 -78 degrees. My tank cycles as low as 74 over night. All of the suddend my tank would not drop below 79. I remembered I had a 12 inch fan inder the cabinet. It had been shut off. When I fired the fanback up my tank temp dropped back down to 76 degrees.
Conclussion: A fan inder the tank to move air does have a large impact to keeping the tank cool. Found my UV was the biggest culpret. Granted evporation is more then normal I find myself adding about 1 gallon per week sometimes even less.
I have the Pacific Imports 1/10hp unit and it works great on a 150. Casey uses the same one on his 200 with about 1000 watts of light and it works great for him also. premium Aquatics and a great price!