Are they both necessary with the use of cast lead bullets and the many types we shoot?
I would think the OAL length gauge would more than suffice.

Same for me as what calledflyer said. I have a dial caliper, and digital 1" micrometer, and they do all I need.

I have both the OAL gauge and an ogive comparator.

They do help me to precisely duplicate any exceptional load I have developed.

With cast bullets there is not as much need since we are using the same bullets cast from a mould.

However different lots of jacketed bullets do vary as to where the ogive may be and these tools allow you to readjust your load to have the same jump to the lands.

"Example, by knowing cartridge base to Ogive length where touch is, I can set a cartridge up on the bench that will have "X" amount of powder compression and "Y" amount of jump or jam before it's chambered."

Bear with me. If I use the Hornady OAL gauge, I will use the lands to stop the bullet at its ogive. But I measure from base to tip. I can see some loose measurements with sharp spire point bullets but any with meplats should be very accurate. 
If I use the comparator, I use the measurement of the ogive and use this measurement to duplicate loaded rounds. 

Both of them sounds a little superfluous.

Red Cent wrote on Mar 15^th, 2019 at 8:42pm:

I agree and that’s why I don’t bother with overall length.

For the most part, base to tip is a needless measurement. The only function it serves is to make sure a round will fit in a magazine. The measurements that matter are how far into/out of the rifling the bullet rests when chambered, or how much is or isn’t in the case. 

Cartridge overall length is based on SAAMI specs which need to accommodate magazines and cylinders, and it can be measured with a simple tool. The problem is bullet profile. Not every bullet can be loaded to “spec” without either falling out of the case or jamming the lands. 

The problem with the overall length measurement, is a much bigger problem jacketed bullets than cast because of the way the bullets are made. Not uncommon to have .010” length difference between longest and shortest bullets in two lots of bullets. Or they can be the same length and have that much difference in bearing surface length or base to ogive.

That means using a COL measurement could result in rounds that will load anywhere from a .005” jam to .005” jump when what you wanted was a touch. 

Since they are loaded by being pushed by the ogive of the bullet, overall length will vary. If overall length is the same, seating depth will vary.

So for me, I basically ignore overall length, unless there is a magazine or cyclinder involved and only concern myself with cartridge base to ogive. Unless I need to give load data to someone with a different rifle. Then I give overall length, and the jump or jam. Example, this is the exact bullet, loaded at 2.345” and that is .010” off the lands in my rifle.

All that to say that the over all length gauge, is a tool to give you a “standard” made from your case and bullet based on a specific chamber. It can be measured many ways

Measuring it with a comparator at the ogive, gives the length a meaning. 

Overall length works great if your bullets are uniform. The less uniform they are the more a comparator will help.

Red Cent wrote on Mar 15^th, 2019 at 11:26pm:

In a perfect world the insert is designed to touch the same place on the bullet that would contact the rifling, the smallest diameter of the lands.

As long as the bore riding portion of the bullet is less than the diameter of the hole in the insert it will work.

I have had a couple of bullets that are cast oversized because the bore is old and worn or maybe cut poorly, that I needed to enlarge the opening to match the bullet.