As Charlie said they're not the same. The combiner just shorts the two batteries
together when a charging voltage is sensed. The Echo Charger
If your charging source never exceeds 14.4 volts these two devices are going to function very much the same, except that the Echo supposedly will never allow more than 15 amps through it, which is a non issue unless you have a badly depleted start battery, at which point the combiner is probably the better choice.
If you have something like the Balmar 612 regulator
, it has programs where the bulk charge stage can be a higher voltage, some built in programs are 14.8 volts. So a discharged house bank could sit at 14.8 volts while the start battery on a combiner which probably is mostly charged already will be getting overcharged. The Echo states it will never exceed 14.4 volts to the start battery.
When the input voltage is 13.0/25.5 volts DC or higher, echo-charge
automatically switches ON. The LED glows a steady green. When the
input voltage is lower than 13.0/25.5 volts, the echo-charge automatically
switches OFF, and the LED blinks green. The output voltage of echocharge
is limited to 14.4/28.8 volts. When it reaches 14.4/28.8 volts, the
charge current will decrease, maintaining a float condition. The starter
battery will be fully charged without overcharging.
No load current drain on the house bank is less than 50 milli-amps.
If the input voltage is above 14.4 volts (or 28.8), output will be limited to a
maximum of 14.4/28.8 volts.