I exclusively use Nanos for the dropController and the ones I build are the same as the one in the photos in the build guide. I also almost exclusively use them in other projects as well.
Although other types of Arduino can be used, the dropController was designed around the Nano.
I buy clones very cheaply direct from China and I try to get the ones with the CH340 chip rather than a FTDI chip. These are often sold as “improved” or “latest” versions. I think the last batch (20 pcs) cost me aound $1.20 each (USD) – like this one: https://item.taobao.com/item.htm?id=554818138175. Unfortunately Taobao is not really available outside of China.
I have never had any problems with the clones except my own stupidity (I have a habit of shorting them).