How are you measuring COL? If its from point to base the better calipers won't make much difference. If your measuring from base to ogive then it definitely will.
One improvement is that what you are looking at will last your lifetime, if you aren't a clutz and drop 'em on a regular basis or use them as a wrench.
Whereas the 29.95 Harbor Freight stuff will need to be replaced every 5 or less years if used regularly. 150/$30 = 50 bucks every 5 years. At your age it'd be worth it. @ my age I'd be wasting a hundred bucks.
When I kick the bucket I want all my tools broken down and worn out all barrels shot out and tired from shooting so far, be dead broke (pun) and the horse to find its way home.