Challenge coins. Do you use them, collect them, or both?

Only coins that ever mattered to me were ones with an EOD crab on them and that was mostly so I didn't get coin dropped

I'm giving you a thumbs up for the BIRF SOC photo.

Nope, never had them when I was in. A "Thanks for a good job" or a letter of appreciation was all we needed. Hell, we didn't have enough funds to pay for shit paper! No diesel for the trucks! And we gave a shit about some "coin" that is the military's answer to Hallmark? What a waste of money.

I have a collection of them. They range from the III Armored Corps Commanding General to the SGM of the Army (Long story for both, so not here). All of them were directly awarded to me with the "secret handshake," from the person whose coin it was. All of these I consider award coins.
Despite how high ranking some of them were, the one I am most proud of, and still carry, is my 2nd ID coin. It was awarded for being in the combat division. It served the purpose the original coins were for. I see it as an actual challenge coin. In my eyes, the others are not.

I ran into one Ammo troop at Bush Intercontinental airport who coined checked me, the one time i didn't have my ammo coin, and it seemed like vets and active duty came out of the woodwork at that airport bar. I had a $300 tab by the time I had to catch my next flight lol

I first enlisted in 2006. Here's the Corps as I first knew it:
There was no CFT. The PFT was done twice a year.
You were waived from height and weight standards if you got a first class on the PFT.
Rifle qualification consisted only of Table 1 for score. The other tables were to expend ammo.
You ironed in the creases to your khaki shirts both long sleeve and short sleeve.
The Post 9/11 GI Bill didn't exist just yet.
There was good expectation that you would deploy to either Iraq or Afghanistan at least once.
ISCs had more involvement with computer-related issues and emails than today.
Blackberries were the only smart phones, and you held high freaking status if you were issued one.
Annual training was done via DEATH BY POWERPOINT.
Most of the older command who were in during Operations Desert Shield and Storm had yet to retire.
My first issued weapon was an M16A2. No ACOGs; just iron sights.
Don't Ask Don't Tell was still a thing, but the Corps was a lot gayer then (just my personal opinion).
Loan sharks, for used car dealerships especially, were a much bigger problem than they are now.
Boot camp reference: 3rd Recruit Battalion was based literally in the woods away from the main parts of Parris Island. We even had our own parade deck.
You done f**ked up if your team/squad leader addressed you by rank, first, and last name and took you to an isolated spot for a private chat.
My MOS school had the students from Army, Navy, and Marines train and learn together except for PT and field drill.
You were issued Birth Control Glasses.
It was financially outstanding to reenlist as a musician (5-digit bonuses).

I have a few, a couple given, some gifted from Battles, and a few bought. The one's I bought are from the Forts/Bases I've been to. With the exception of the blood donation coin, I donated $10 for that after donating blood.

I was a bartender after I got out. Had a couple soldiers come in and I gave them their first bar challenge. I ended up giving them both a couple free because I was impressed they 1) knew what it was and 2) actually had coins on them.

Don't fit in the soda machines, so not very useful to me. I jut cherish my coin from the POTUS (W), Wolfowitz when he was deputy SoD, and those from a few Generals.

I still have all of the ones I was presented. The best was from the Secretary of Defense while in Riyadh.