Proportional are the way to go as they regulate the heating element into a tighter band than an ON/Off type will. The On/Off is better than a rheostat or nothing at all. The rheostat is the Yugo (gets you there but you may have to push it at times), the On/Off is the Chevy (It does the job), the Proportional is the Cadillac (Not only does it get you their but in style and comfort). Flex Watt should never be used with anything less than an On/Off type T-stat. Your more inexpensive method will work using the Johnson T-stat and Flex Watt. On the other hand I think most people would rather use a proportional T-stat over an On/Off due to the tighter control it has and the added features of alarms and such available on the Herpstat ND, II, or Pro step them up from the basic Cadillac to a fully equipped BMW convertible.