I used to run a 32 gallon bowfront sumpless.
It was heavily stocked and my first non all in one (biocube/aquapod) salt water aquarium.
The osakas make gorgeous reefs, I run a 95 gallon seamless bowfront myself though so maybe I'm biased.
The Fluval is essentially a sump in many ways, it adds a little water volume and you can hide various additives to it.
I modded a rena xp1 that I drilled a hole in and put the heater in there and siliconed around the hole to hide my heater.
You can definitey run live rock in there as well, rubble is best to provide the most surface area possible for your bacteria.
Carbon is also a great additive to run in there, but you will need to change it regularily as well as clean the canister itself at least monthly.
Buy the best HOB simmer you can afford, Deltec makes some of the best ones out there, this alone will negate any major non cosmetic advantages of having a sump.
http://www.jlaquatics.com/phpstore/store_pages/product-info.php?product_ID=DD-P0500