OMD and FL-14 flash
I have that combo.
The FL-14 works better than the supplied clip-on flash unit in these areas:
- it's more powerful, so more useful for fill flash during daylight
- recycle times are faster
And this about ends the advantages.
Be aware of this one quibble: you cannot fire the FL-14 in full manual control like the clip-on unit, or, to be more precise: you CAN do it, but the FL-14 will always fire at full power (1/1) there's no way to manually set a lower power level like 1/2 or 1/8 or 1/32, etc.
As for size: the FL-14 is really quite small, light and comes with a velvety pouch.
Bottom line: are you looking for a small flash to use in TTL or AUTO that has a bit more oomph than the included flash but is still small and light to pack/carry? If the answer is yes, the FL-14 could be a viable solution.
If instead you are looking for a more capable flash in terms of both power AND functionality (bounce flash, wireless capability, etc) then take a look at the FL-300R and skip the FL-14