I've been pleased with my BIAB/RIMS hybrid. My mash tun is a 5-gallon Igloo cooler lined with a fine-mesh bag sitting on a mesh basket. I use a small pump to recirculate the wort through a heat exchanger submerged in a 3-gallon coffee maker.
I keep the water in the coffee maker about 100 F higher than the target mash temperature and circulate the wort at about one quart per minute. There's nothing magic about using the heat exchanger, it just buffers the temperature swings better than applying heat directly and circulates the wort through the grain bed to reach and maintain an even temperature. I use a couple of digital thermometers to track the temperature of the heat exchanger water and the mash. I suspect using a coffee maker for the heat exchanger is cheaper than using propane. It also lets me brew in the house until the wort is ready to boil.
Once the mash is complete I disconnect the pump and attach a hose to run the wort into my boiling pot. When the wort level approaches the top of the grain bed I drop the pump into the coffee maker (which has been raised to about 1700 F) and begin pumping the heat exchanger water (now the sparge water) onto the grain bed.
About 15 minutes before the end of the boil I drop the heat exchanger (now the immersion cooler) into the pot to sanitize it. At the end of the boil I drop the pump into a pot of ice water and chill the wort to pitching temperature.
While the wort is boiling, I dump the grain out of the mash tun bag, clean the bag and the tun and sanitize them with starsan. I pour the cooled wort into the sanitized mash tun (with lots of splashing) and run it into my fermenter (more splashing) and add filtered water to hit my desired OG.
The system works well. My efficiency is whatever it is and I enjoy the beer. The system is cheap, easy to build, and easy to use. It would be simple to add a thermostat to maintain my heat exchanger water at the desired temperature and to control recirculation during mash rests, but it works to my satisfaction manually. The heart of the system is the pump, available from Amazon (http://www.amazon.com/temperature-approval-coffee-process-application/dp/B004HHW0FU) for $14.50. It's small and will clog if the grain is not kept in a fine-mesh bag, but it doesn't cause foaming and potential hot side aeration. I'm assuming foaming is associated with a higher capacity pump which must be restricted, forcing the impeller to agitate the wort and cavitate.
Dan