Battery load test

Anyone have experince or opinion regarding this consurmer grade battery
tester.
Manufacturer is EZRed. They make a temperature compensated hydrometer
which is very good.
Already using the hydrometer, and digital voltmeter to monitor
condition of my battery.
Just wondering if this digital load test could help confirm when it
would be time to replace before facing a no start condition.
Estimate the 2 yr. old Die Hard with 550 CCA is about 75 -80% at this
time. Center cells show good, end cells lower range of good.
Alternator is working great. Battery voltage 12.7 immediately after
turning engine off, drops to 12.45 V by morning.
The reason I ask about this load tester, is that generally, amp load
needs to be 1/2 CCA. For example EZRed make a 250 amp load tester good
for up to 500 CCA batteries. Yet this one, with fixed 100 amp load is
rated higher.

http://www.batterystuff.com/productd...tml?id=462&c=4

Would only need to use it occasionally, so don't want to buy a large
shop quality tester, yet would be nice to have one of these if
worthwhile.