Thanks for all that info Woodinblack and Quatschmacher - really appreciate it.
From the comments so far, the SY-1 feels like it's going to be my first choice, given its ease of use, compact form factor as can be seen on Al Krow's board, and the fact that it is fair bit cheaper than both the C4 and FI.
But based on what Quatschmacher said that on a bunch of key matters the FI blows the C4 away, the FI would seem to be the one to go for next. Very helpful!