been offerd 1 for my 600rr was just wondering do i need a power commander?
not necessarily if you can handle the farting sound, lol…
so does that mean yes?
All depends how good the ECU is on your 600RR is?
I’ve got a power commander and akrapovic on my FZ1 because
the standard ECU is set up to starve the engine at 3,500 rpm
to make sure it passes EU emission rules. The standard ECU
combined with the lardy great cat makes it sound like a sowing
machine and run like a rabbit with hiccups (at 3000 to 4000 rpm).
Now it pulls smoothly all the way from low revs, screams all the
way to the red line in all gears, farts like god on the over run
(as someone said on LB earlier). The mechanic that services
it said, “it makes a lovely burbling sound”, and it uses far too
much petrol 
I’ve not bothered with a power commander on my SV as the
ECU is ok, it runs fine and sounds great with a MIVV can.
well i fitted a race only pipe to my gixer a few years back and had a yoshi box plugged into and run on the dyno to make sure all was running well and ironed out any glitches worked out 99 quid all in, that was at hm raceing, far cheaper than a power commander
I think the Yoshi box is a plug in ECU that will override
the standard Suzuki ECU for some older GSXRs.
A Powercommander is also a plug in ECU that will override
the standard ECU and is available for most makes and models.
If they are the same thing and the Yoshi is cheaper then
go for it (if you’ve got the right model GSXR)
As I said though, some newer bikes have good enough
ECUs, e.g. the R1 can be switched to sports mode, etc,
so that you do not gain much, if anything, from overriding
the stock ECU.
And you’re right a Powercommander is expensive.