the twin package you have linked to is imo a fair deal, but it does have its drawbacks.
firstly the amps output is only 2x 150watts bridged into 4ohm's,(which is half the subs rated input power).
the wiring kit is only 8awg power cable,(rated at 40amps over 5mtrs before voltage drop becomes an issue).
if you can purchase the above kit with a 4awg wiring kit and a JBL GTO 75.4 amp then that would be a better option. however, if your planning any future upgrades then the JBL GTO 4000 is ideal for bridging into two ch's to drive a set of front components, this would then require you to purchase a suitable mono amp to drive the GT4's,(JBL GTO 600.1 or GTO 1201.1), but this would then mean the present wiring kit,(either 4awg or 8awg), would be inadequate,(best value 0awg kit is the Autoleads PC4-28 at under £50).
you really need to balance your expectations against your actual budget.
as an example heres a few links to a much heavier setup using items purchased singularly from different sources.
subs
2x 12" JBL GT4's---price here is for two subs.
http://cgi.ebay.co.uk/BOX-OF-2-JBL-...9QQihZ012QQcategoryZ18805QQrdZ1QQcmdZViewItem
2x sealed enclosures---can't link to these, but motorworld are currently doing 12" sealed enclosures at £19.99 each.
wiring kit
http://cgi.ebay.co.uk/Autoleads-PC4...2084380QQihZ014QQcategoryZ14932QQcmdZViewItem
amplifier
JBL GTO 75.4---gives 2 ch's bridged at 300watts rms
http://www.caraudiodirect.co.uk/jbl-gto754-p-4140.html?cadid=c415b1a525ee5f7d57f9afda62c24732
or ebay
http://cgi.ebay.co.uk/JBL-GTO-75-4-...85QQihZ002QQcategoryZ4950QQrdZ1QQcmdZViewItem
if your still struggling to decide on what to buy, i would suggest you try to find the local meeting place where all the car audio guys go to play their systems. i can only offer advice as to what i would go for, but my tastes will differ from yours, by listening to other setups you will get a better idea of what is required to achieve the effect you desire.
i would assume a good place to start looking and listening would be your local caraudiosecurity outlet, they should have various demo units setup that you can play with.
i could have popped over on monday,(but failed to get play off tickets for wembley
), and let you loose on mine, but as it stands at the moment i won't be travelling.
any more questions then ask away,(far better to make an informed purchase rather than an impulse purchase that will be no use as or when you decide to upgrade).
HTH mate.