The trees are drawing me near, I've got to find out why?
Those gentle voices I hear, explain it all with a sigh.
"Tuesday Afternoon" Moody Blues
Even duct-tape can't fix stupid.
So use what you are comfortable with and replace them when they need to be replaced. Every so many feet of stitching is a good factor, but again... I can't give you a good rule of thumb (see the above discussion). If it "pops" I would think a new needle would be in order. You may be able to gauge the point of a "sharp" with the same fingernail test for a sharp blade. The universal needle and the ball point will not respond the same way.
There you go... clear as mud. That's why this discussion is in the video titled "Beyond the Mysteries" or something like that.
I may be slow... But I sure am gimpy.
"Bless you child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way."
Mrs. Loftus to Huck Finn
We Don't Sew... We Make Gear! video series
Important thread injector guidelines especially for Newbies
Bobbin Tension - A Personal Viewpoint
Useful thread and timely too
Just bought my own thread injector yesterday, £100 Brother from one of the catalogue stores. It's nothing fancy but I hope it'll do me for what I want.
I called into a crafts shop today and didn't have a clue what I needed so walked out empty handed