They are expensive.   I made without a set for at least a decade after someone here recommended them.
I decided I'm not falling for some stupid overpriced German pliers, especially something so specialized.

I've never been more wrong!

The things are pure gold - they're worth EVERY PENNY! They'll pay for themselves the first time you (don't) crack a lower, but more importantly, I was dead-wrong about parallel-closing jaws being 'specialized'.  I catch myself using 'em (instead of pliers or vice-grips) all the time.
The only thing I regret is not buying a set twenty years ago.

I know they're not cheap, but they're so rugged they'll last a lifetime (or more). Not like something you'll have to replace every few years.

Yes! 

Every new builder should add one on to their next Amazon order (or keep an eye out for one at Lowes, Home Depot, or wherever).
Even a "universal" 1/4" clevis-pin with multiple holes saves a lot of headaches (looking for front TD pin detents launched into orbit). 

Best 79 cents you'll ever spend.

                                        

   
  
                   

BIG +1 on the KAK Walt's Tool....

http://www.ar15.com/forums/t_3_4/362116_How_to_install_the_front_Pivot_Pin_using_a__1_clevis_pin___56K_death.html

This is outright plagiarism from @Desert_AIP , but  I think he'll forgive me.

This is one of the best tips I've ever seen posted on ARFCOM.
It's certainly not a "necessary tool", but it's makes my life a little easier by turning a 5-minute task into a 20-second task (no doubt it also saved a few detents & springs over the years). YMMV
Most importantly, the tool  is practically free.

   ___________________________________________________________
"If you are only doing one build, it's hard to justify spending money on a single use tool, if you're building 100 the technique below works
equally well.  
Many here have talked about using a 1/4" clevis pin to install the Pivot Pin but there are always follow up questions as to
the technique.
Below is a step by step procedure to install the Pivot Pin using a clevis pin, this takes 10 times longer to describe than to
actually perform and costs nearly nothing.

Got to your local hardware store and buy a 1/4" clevis pin.  Get the kind with at least
one hole through it not the kind with a captured ball bearing on the
end.  
I use a 2" long pin which reaches completely across the front of the lower.  Get one at least this long.  I paid 65¢ for mine.


Insert the clevis pin through the pivot pin holes in the front of the lower from the left side.
Align the hole (or one of the holes) in the clevis pin with the pivot pin detent channel in the lower.


Insert the pivot pin detent spring through the hole and into the channel in the lower.


Insert the pivot pin detent through the hole.  The spring will not let it go in very far without pressure.


I perform the next three steps inside a 2 gallon zip-loc bag so I don't lose the detent or spring in case it gets away from me.

With a punch or other suitable tool (like an allen wrench) push the detent
through the hole in the clevis pin and into the lower while compressing
the spring.  The detent and spring are now inside the lower and clear of
the clevis pin.  The only thing holding them in place is pressure on
the punch.


Turn the punch or allen wrench 90 degrees counter-clockwise so the hole is
now at the top of the clevis pin.  This will capture the detent and
spring along the side of the clevis pin.  

 
Remove the punch.  You can see the detent poking out of the hole.


Start the pivot pin into the lower from the right side.  Make sure the groove in the pivot pin is at the top.  


As you push the clevis pin out of the hole, keep sideways pressure on the detent until it is captured by the pivot pin.  


Keep pushing the pivot pin though the right side pivot hole.  Once it is in
the hole and won't fly out under spring pressure, remove the clevis pin.


Rotate the pivot pin 90 degrees counter-clockwise until the groove in the pivot pin captures the detent.  


You are finished!  "