There are many types of heaters. I found mine on Drs. Foster and Smith, I think they all pretty much work equally. I use the Jager on my 35 and a Hydor on my 10. Both seem to work fine, but I live in very warm weather so they don't have to be on constantly.
Also, yes, it's bad for the light to be on 24/7. Fish need time to rest, and they do this in darkness. Fish can't close thei eyes and block out light like mammals can. It's good to emulate nature, with roughly 12 hours of light and 12 of dark. This can of course be altered as needed, especially to control algae.
Constant light will put fish under stress as it's not natural for them, and will make them more susceptible to disease. This is especially true for nocturnal fish (kuhli loaches come to mind), as they prefer to be active during the night.