I use a RIMS tube with electronic controller using a digital temp probe on my 20 gal system. I can shed some light from personal experience. The key thing is having a electronic controller to regulate the heat and not just by monitoring the temp and shutting off. You want a lower wattage on the heating element in the tube. This prevents it from heating up too fast as the heated wort needs to travel back to the top of the mash tun, onto the grain bed, back through the grain bed and then back out past the sensor in the tube. If the sensor is still just reading what hasn't been effected yet with the recirculation then it will throw off your temps. You only want the the heating element to be hot enough to gently bring up the temp it it drops. This require you to use a 4500 watt low density heating unit and you must have control of the power going to it, it can be analog or digital. But it works great.