powered subs/built in amp

are powered subs with built in amps decent at all ?
mainly because i am very distressed on space and im in a convertible and am only looking for a small amount but more bass to go with my car
its also a much better price then subs/box/amp/wires/installation
when these things cover pretty much all of that
here are a few examples (ebay examples but just want an opinion)

http://cgi.ebay.com/CLARION-SRV303-7-INC-POWERED-ENCLOSED-CAR-SUBWOOFER-SUB_W0QQitemZ9702928484QQcategoryZ32822QQrdZ1QQcmd ZViewItem

http://cgi.ebay.com/KENWOOD-KSC-WD250-200w-10-POWERED-SUBWOOFER-SUB-BOX_W0QQitemZ5881422065QQcategoryZ32822QQrdZ1QQcmd ZViewItem

http://cgi.ebay.com/KENWOOD-KSC-SW1-DUAL-6-5-ENCLOSED-POWERED-SUBWOOFER_W0QQitemZ9700751018QQcategoryZ32822QQrdZ 1QQcmdZViewItem

http://cgi.ebay.com/INFINITY-BASSLINK-X-10-POWERED-SUBWOOFER-INSTOCK-NEW_W0QQitemZ9702702937QQcategoryZ32822QQrdZ1QQcmd ZViewItem

http://cgi.ebay.com/INFINITY-Basslink-T-10-Powered-Subwoofer-System-NEW_W0QQitemZ9701713014QQcategoryZ32822QQrdZ1QQcmd ZViewItem

kinda long but thanks

actually this one is probally the best for the money

http://cgi.ebay.com/ebaymotors/Audiovox-BA-100-8-Amplified-Subwoofer-Bass-Tube-Box_W0QQitemZ8048509205QQcategoryZ38647QQrdZ1QQcmd ZViewItem

One of the kenwoods, or the infinity setups, audiovox has never been know for good audio equipment.

i'd advise against the audiovox. my friend had an audiobahn tube which gave him the bass he needed, but sounded terrible. it blew out and he's looking at the first kenwood you listed.

i would do kenwood or infinity but they will never sound as good as a sub in a box does becasue they are cheaper made and thats why they cost alot less. you get what u pay for.