From that post, you were comparing a device attribute against a device attribute, and it sounds like there may have been a bug with that. It doesn't match this use case, where a device is being compared against a fixed value.
The normal rule above would only send the on commands when the truth changed from false to true. If it was changed to a triggered rule, it would send the on commands every time the temperature updated and it was below 68 degrees. The net result may be the same (commanding a device on when it's already on doesn't hurt) but that's a lot of unnecessary commands being thrown around.
This is a pretty basic rule, so I think we need to figure out exactly what's happening rather than trying to change the execution strategy.