You'll see decent performance in the center of the frame, but pretty bad CA and spherical aberration at the edges of the frame. Open the large version of the far left bug image, and look at the right edge, the clover petal tips, you'll see what I mean; see the heavy blue fringe?
The pics were taken with a Sigma SD9 per the EXIF, and that's really only a 3.4Mpx camera (even though Sigma marketed it as 10+Mpx) but due to it's special sensor design it outputs images with detail more like 5Mpx or so. You should get results at least as good with the XT.
On a very tight budget, these will produce decent macro performance. There are much better versions available, using two glass elements instead of the single element these use, but they are more expensive (look forCanon 250D and 500D).
Another good option for macro is to buy some extension tubes, but you really should use those with a prime, like the inexpensive 50/1.8 perhaps. The combination of the tubes plus the 50/1.8 will run about $240, though, about 2/3 the cost of a dedicated macro lens.
All in all, for $23, these should provide satisfactory performance and give you some experience shooting macro. If, down the line, you want better performance, you can then make a decision as to which path is best for you.
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