The 108181 is a "mini" grinder meaning that it has a smaller diameter wheel, 4 1/2" vs 5 7/8", which will have a more dramatically changing radius from wear right from the start. This is significant to you because centering on a pivoting head grinder is affected by wheel diameter. Another thing to consider is that the mini grinders that I have tried all had a higher rpm motor than the larger grinders and even with the smaller diameter wheel, it seems evident that rim speed is higher because they are more prone to burning a tooth. The small grinders are also less powerful which is a factor in feed speed of the wheel against the tooth. There is an optimal ratio of metal removed vs heat imparted to the tooth that is hard to achieve with the minis. The mini grinders are also built less robustley than the 511s and are easier to flex out of precise angular alignment and they lack an adjustable chain vise that allows you to grind the 10° topplate angle on chisel chain. The head angle is not adjustable on many of the small grinders either and I believe this is also true of the 108181.
Russ