There are LOTS of USED OIL heater manufacturers. Waste Oil is a ugly term as it implies hazardous waste. Even the Used oil heater companies use it, because that is what everyone calls it, but they prefer USED OIL.
Anyhow, I do not have one, yet. I have been looking for a couple of years now, just cannot get off the dollars for one.
Omni, I suspect, makes a good product, its just tough to get past the sales hype and the BS artist sales people they have (if you talk to them on the phone)
A couple of major things sets the various brands apart. All require compressed air, some have their own onboard compressors, while others depend on shop air (regulated down to about 20 psi) instead of providing a onboard compressor. I am not willing to leave the shop air system (when it is fully installed) turned on just to run the heater when I'm not in the shop. The other item, which may or may not be a factor, is that some of the heaters are designed to be connected to a duct system, or left un-ducted, While others have louvers and cannot and are not rated to be ducted.
In looking at heaters I found the following manufacturers.
Reznor, which is an old manufacturer of heaters, now owned by Thomas & Betts and who decline to post the location of their headquarters or manufacturing facilities.
http://www.reznorheaters.com/
Firelake, Mt. Crawford, VA
http://www.usedoilheaters.com/index.html
EnergyLogic, Nashville, TN
http://www.energylogic.com/heaters.html
Heatwave which is also found under the name Siebring Manufacturing, George, IA
http://www.heatwave-waste-oil-heaters.com
Clean Burn, Leola, PA
http://www.cleanburn.com/
Lanair, Janesville, WI
http://www.lanair.com/Lanair2.0/
Omni by Econo Heat, Spokane, WA
http://www.econoheat.com/
Norki Energy Systems, Poughkeepsie, NY
http://www.norki.com
Units without onboard air compressors are Clean Burn, Firelake, Lanair, and Heatwave/Seibring units.
Norki, Omni, EnergyLogic and Reznor all use built in air compressors.
Some of these brands share burner systems manufactured by a third party, Siebring I think, others use their own design burner systems.
Reznor seems to be the only company that manufactures a full line of heaters, used oil, fuel oil, propane and natural gas.
Charles