Yes, I start the motor on the stir paddle that mixes the hot mash water at 7 RPM then I open up the bottom drawer on the hopper to let the grist trickle out at whatever rate looks good... I use a insulated aluminum bubble blanket (not shown) you can get at the hardware stores around the mash tun once I mash in... It can only go on once the hopper is removed. I can hit the usual mash temps (140's to 150's) and it holds there pretty good for up to 2 hours... I think it might drop 1-2 degs over 90 mins with 100lbs of grain in there (lot of thermal mass)
I made the hopper because mashing in 100 lbs by hand is a lot of work and you loose a lot of temperature... I have a split lid which is not shown... it covers the mash tun when it is mixing so I don't loose too much heat... it is made out of plywood and covered with oak vineer. It usually takes 30 mins to mash in and I don't get any large dough balls.
I can do a step mash with boiling water infusions, but it is hit or miss with this system so I usually stick with single temp which is great for ales... I also do this for lagers and they seem pretty decent also.
The most I have ever done in that tun was 120lbs of grain.