Actually your wrong on every count. You can get better results with a prommy or pdi barrel because they are straighter. A miracle barrel is just a 6.06mm barrel with an insert in to aid centering of the bb, a firefly bucking works better when combined with either of the barrels mentioned above and I even got better results with a cheaper zci barrel. Wont have any real effect on fps, range is affected more by hop than anything else and accuracy depends on half a dozen things all making a small difference.
As for expensive and hard to get
http://eagle6.co.uk/shop/catalogsearch/result/?q=MIRACLE+Inner+Barrel