I personally think the metalic stickers are pretty solid on gunpla. They are usually placed between two bits of clear plastic so there is no fear of them falling off. Here's an example on my recent picture with a sticker inside the head right at the top.
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Of course if you don't want to they are optional
The water transfers in my case is more that I think they might make an uneccessary mess of detail. Perhapes I might use them on the shields?
EDIT: Unrelated to comment but just on a side note, my thoughts on the thunderbolt kit itself. It was great fun to build but took a heck of a long time with all the extra armour. Still though this was probably my favorite one, now I have my PG Unicorn next which is a completely different beast to tackle.