I hope you're just using it as a temporary proxy because that looks extremely out of place. It just looks like an hulkbuster armor with gun bits glued to it. It fails to capture the tau aesthetics and just looks like an out of scale toy, honestly. Just lose some time looking at tau stuff and trying to analyse what makes a tau battlesuit, a tau battlesuit. What design elements are present in all tau suits and how you can reproduce them. Then use the hulkbuster armour as a base, since it's proportions are cool, and add the extra shapes on top of it. Don't shy away from digging out parts of your model and rebuild them with a more tau look. Please see this as constructive criticism and not as bashing.
Exactly. It's a toy with some 40k
guns glued on, not a real conversion. It's fine to use toys/non-40k
model kits/etc as parts in a conversion, but you need to convert
those parts. Break up the shapes, replace obvious non-Tau elements like the giant cartoonish fists with more appropriate parts, integrate the weapons into the design instead of just gluing them on in a random spot, etc. And, as a general rule, your motivation for a conversion should be "this will look really awesome" and not "this is so much cheaper".