freaks come in different front colours too - although most stores only seem to show black fronts on their websites, they come in around 6 colours, gloss and dust.
the freak kit essentially gives you 8 barrels in one kit, as you can change the bore size to match your paint - this is one of the greatest keys to accuracy.
with an ion, i wouldn't bother with a barrel over 14" to be honest. a 20" barrel on an ion would, as you say, be a tad silly.
how long have these friends of yours been playing to give you the advice on the barrel? and what marker do they have the 20" barrel on?
the progresive is a good barrel. it has a progressive bore (thus the name) which means that it has different sized internal diameters as you move along the barrel - the theory being it will allow most paints to get at least some match as the ball travels. it works to some extend, but not as well as a dedicated bore sized barrel.
also, your choice of barrel will come down to what type of paintball you play.
on the sup'air field most folk will over bore (barrel bore bigger than paint size), losing a little accuracy in favour of avoiding bursts in the barrel and screwing up your play for those few precious moments that can make all the difference. so a single larger bore barrel may do, although a kit with a around 3 bore sizes would be better.
on the scenario field where there is more of an emphasis of the mythical one shot kill (i never shoot anyone once....you can never be certain one ball will actually burst!!) then a closer barrel to more match can be considered more important.
