Your price for an FE is nearly double what I would pay... that may change whether DIY is more expensive than pressurised.
Pressurised is a lot easier to get stable CO2 levels with though, so can be recommended just for that alone.
Your nano diffuser will work fine.
The first ebay item you showed linked is not a reg, it looks like a needle valve to me - which is what you can use inbetween a reg and diffuser to fine tune the co2 level.
The second item would work, but with only one dial it does not give you as much info as a two valve reg.
One dial tells you the amount of gas left in your FE.
The other dial tells you the amount of gas you are letting out of your FE.
I do not know which of the two dials this reg provides.
When I ran pressurised I used a cheap aquili reg that had no dials at all!
I used to tell how empty my FE was by the weight of it.
I used to set my output by trial and error.
Worked fine for me.
I also did not run a solenoid and built my own cheapo internal reactor. That brought the intial investment cost down.
Each to their own though
Have a look around with the search funciton, there are plenty of posts on here already discussing which kit to buy and the pros and cons