You are absolutely right.You are probably right about lasting longer under smaller loads and the fact that there are no moving parts. I think my thought was more about possibly being near the load limit shortening the life of the SSR.
Something important to consider is the size of the tank, and the wattage of the heater (or lights) you plan on using. My tank for example has 2x 350 watt heaters which are 3A each. Those would be a problem for 2A relays.
Either one will most likely work for most people, but if you have a larger tank I would go with mechanical relays.
Here in r2r , we have lots of people with larger tanks (180G+), so its likely they have heater/chillers that draws higher than 2A current
