The skimmer is really great for an HOB and only takes about 3-4" of space behind the tank....it pulls out lots of smelly stuff from the water, I was surprised!
As for surface skimming, the pumps combined with the spraybars from the renas help break up that. Obviously it won't be as good as surface overflow as with a sump but very manageable.
This is a personal opinion, but many(not all) sumps have several things that I dislike. Firstly, i find excessive evaporation with sumps with a neccesity to keep up on top ups for feer of running air into the pumps. Secondly, salt creep, because of the water movement and splashing in a sump, there tends to be saltcreep on many surfaces, including the stand in which the sump resides...Thirdly, fairly poor mech filteration, most sumps have little to no mech media...many have just a drip tray on which floss is set....I find one layer of floss tends to let a lot of crud through. Fourthly, noise...I find many sumps way to noisy in both water movement from the overflow and into the sump to pump humm noise. Lastly, the danger of overflow/leaks. IMO, the less holes in your tank, the better. Also, plumbing over time can develop leaks or can suddenly develop leaks. I prefer a filtration system that is contained and safe. For all the above points I mentioned, there are sump designs/top off systems that help or negate those problems, but with many sumps, these problems are still commonplace.
Again, these are my personal opinions, many will disagree and tell you sumps are the way to go. So really it is up to you to decide.
