Your erratic temperatures could be a function of the size of the pellets you're using. How long are they? The longer they are, the less consistent the feed is to the burn pot. Causes wide swings, especially in this hot weather.
The CS pellet engine on the lowest (manual) setting, on that small size 420 grill, will produce a cooking temperature about 110 to 120 degrees above the ambient temperature. So when the weather is 90 outside, your minimum temp is 200 to 210. The digital MAY be able to control a little lower than that but you need a certain amount of pellets in order to prevent a flameout.
Now for your smoke flavor, pellet grills just have a "different" type of smoke flavor than a stick and/or charcoal burner. I've had my CS570 for a year now and have tried extra smoke boxes, add on smoke generators, changed the air outlets, etc. There's just no way the two cookers will ever taste the same. Now that's not to say the pellet grill flavor is bad, quite the contrary as they win lots of contests. But it is certainly different. There are other threads covering this topic on this site as well as on Pelletheads.com. Good luck!!
American BBQ Systems model All Star, CS-570 & TG-300 pellet grills, Broilmaster P3, and lastly, Superfast Red Thermapen