I always write the comet's corner for our German magazine "Sterne und Weltraum" (stars and space). For some time in the past I had to give the estimations of 21P on base of the last apparitions: These were way to bright. The comet developed slower than expected. But now, it has become an real rewarding object.
I obserserved it form a rural site wit my 12 inch Dobsonian and found a well condensed, quite large (4') nebula with hint of a tail. I saw a stellar condensation. If weren't lucky withC/2017 S3, try this one: It is high in the sky and in the near of the milky way, a prominent surroundings. I nearly cressed the North America Nebula some weeks ago, but it was very weak at this time.
North is up in my sketch.