Hey
I like your question and there is a simple answer to it: Its simply overkill. You dont really need the bamis passive. Also you build path is all about movement speed so it would be overkill to buy a item that gives you time limited movement speed. I think they buy it in pro play because its a safer/easier way to play around this time limited movement speed. For learning this pick its surely a good item because you know when you really want to go in and when not but if you really want this just go shurelyas.

Edit: I also forgot to say that Im still not finished with this guide. I planned to explain more detailed what to build and when to build. I also want to explain why you should go these runes and when you should go these runes. But everything has their time so I wait until I have enough time for it :) I hope you understand why you can build Turbo Chemtank but its not your best option. I maybe do a little Q&A part into this guide so if you or someone else has any questions just leave them down here :-)
Have a nice rest day mate!