I can hand file a chain six to eight times before it needs a grinder to even things out.
I was taught to look for "glint" when sharpening a chain. To get an idea what that looks like, take a pocket knife and put the cutting edge to light. Sharp edge does not reflect light. Dull edge reflects light.
It really is as simple as that. Now look at new chain cutters, look at your old chain and see the glint reflected off your cutters.
As for the Timberline sharpener, it is the best sharpening accessory I own, bar none. I have an Oregon grinder, Granberg, that Husky guide above and the Stihl file guide. They all have their place.
This weekend, I was using a chain that was sharpened with the timberline that I bought last month, and I was cutting crotchwood at a local Methodist Church for their firewood program. The chain have been rocked previously and I brought it back with the timberline. I was getting 2 - 3 inch noodles on oak crotchwood I was preparing for the splitter.
Only other advice I have to give is get at least a half dozen chains. They are a consumable item. It is faster to replace a rocked chain than take the time to bring it back while working.
If you throw a chain off the bar, I would think twice about putting it back in service. Deformed drive teeth ruin a bar quickly. Put these chains aside and get a chain breaker with some splicing links. If the chain is fairly new, shorten it up or cannibilize another chain for links and remove the bad links, (those that don't fit in drive groove) Bars are expensive and will last a long time if used right. Bad chain used is false economy and will cost you more than what you're saving.
If you can afford the timberline sharpener, do it. It is the only sharpening accessory that will get consistent factory new results every time. Especially for an inexperienced person. A badly rocked chain will need a grinder, other than that, each accessory has its place and time.