It doesn't matter what brand or what size heater you buy they will all eventually fail. Some will fail a lot sooner than others. For this reason I would recommend running multiple heaters. When one fails you will have a backup.
Hydor ETH heaters are inline heaters. They have a good reputation (with me at least). But depending on the filter you are running and the size tubing the filter is made for the ETH can restrict the water flow through the filter. They would also add undue complexity for running multiple parallel filters.
Their are some nice DIY inline heaters in the DIY section that use conventional submersible heaters encased in PVC and used inline with your external filter.
I prefer conventional submersible heaters in a wet/dry sump myself.