I know it seems like more work but why not work on them as separate parts? The commercial people who put these things together as kits seem to often do such a lousy job!
Its just that these forums are so good at helping you research these individual pieces of hardware, that it just seems ashame not to take advantage of it! Starting with the tank, I've realized that there are people who take home any old tank and later realize the glass quality is not all that great, it waves or its bubbled or chipped or too thin or whatever. I don't know what to advise (I've seen some recommend "all-glass" which I guess might be a brand available widely, or some of the "kit" people also use good glass..)
Then there's the heater, which I'd place as the easiest to get an ok product of, compared to lights or filters. Lights might require a touch more care, with issues of how -much- light you want, to meet your plant goals. Then finally, the stakes jump way up, in my opinion, for the choice of filter. Filters are just very core to the hobby and it just seems a real shame to assume a commercial kit will have a decent one... and only find out later its not and have that mess of having cycled the wrong device for your long-term need!
I realize if you're the type person more interested in the fish themselves, or the look of the aquascape from an artistic standpoint that perhaps taking time to research hardware (or water chemistry for that matter) may just seem like the most boring thing on earth. Anyway, that's my little speech, lol, so I'll shut up now!

Its just that sometimes I can't help but hope that we detail nerds can interest someone in the nuts and bolts... (ok, I'm fading out)
~~waterdrop~~