Sure you could do just that.
I've never seen one of these units up close, looks like you get a lot of nice features, but I wonder how efficient the skimmer is.
I assume you'd be using this on a 55 gallon ?
Flowrates seem a little low to me on their sizing page - but that's just me. If you went with the 75 gallon unit on your 55 - that would give you 300 gph - about 5-1/2 turns per hour - not bad at all.
Sometimes these package deals where you get a lot of features are not always the best, although this may not be the case here.
A "good" return pump, a "good" overflow, some hoses, tubing, clamps and something to hold water is all that is needed. I prefer to put my money in the pump and overflow.
Paying for biomedia and a wet/dry/sump designed around using biomedia, only to remove it when you install it - seems like a waste of cash to me. I've gone down this road before.
But all in all - if you're looking for a complete plug and play system, and it will fit under your tank - just add a good return pump and you'd probably be okay.
HTH