I personally don't think optiwhites are worth it in nano form, yes the look is slicker but side by side with water the differences at this scale are negligible. Ask your LFS if they can make you a tank to your required size, I was quoted £17 for a 1foot cube, of course that's sans lighting but it's a huge saving compared to the £100+ pounds you'd pay from some manufacturers or the £80 ish you'd pay for a similar nano from ADA. Of course take your pick and decide which is for you but if this is your first tank and you don't want to splash out loads then an off the peg from someone like clearseal or a cheap custom through a LFS is the perfect way to go.
Of course what ever option you take an external is what you'll always want on a nano, not just for aesthetics but to increase water volume and stability of the water quality so factor this in, don't get disheartend by their expense, know where to look second hand and things like the ehiem 2213 can be found very reasonably.