I used to roast my own until my source for green beans stopped selling them.
The problem with the hot air popcorn popper method is you can not control heat. You get what you get. The second crack comes too soon.
You would have better results with a new, never used cast iron skillet on the stove top. Stir and shake constantly until the second crack. At that point I lower the heat slightly and go by color.
Once finished immediately pour the beans into a stainless colander, run outside and start tossing them to cool and remove the chaff. Keep tossing until completely cool. A quick cool down is important.
Allow them to set for a day at room temp before grinding or they will be oily and sticky.
It's trial and error until you fine tune your process. I was disappointed with my first batch but after trying different pans and heat profiles I was brewing a fine cup of joe.
On Edit: The most common mistake is roasting too hot. If they look burnt in 5 minutes you were too hot.
Take an analytical approach to this. Realize what you did and adjust your technique to improve your product. Take notes if needed.
I found it took more grounds to make the same strength as store bought coffee. I do not know why but this was consistent.
My flavor was different from anything store bought. Not better or worse, just different. It was smooth. Same with my home brewed ale. You can't buy that flavor in a store.
A french press will bring out more flavor.
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