Don't hesitate to do a search on "tablet" in the forums, you'll see plenty of feedback.
Generally speaking, a graphic tablet is mostly useful to convey your pen-and-paper drawing skill to the computer.
For pixel art, it's mostly useful at the beginning, to get the right proportions and movements, before the pixel-by-pixel detail. It may be a small part of the work time, but it's important - it's very frustrating when you have a clear idea in your head and you can't do it with mouse.
Even if you use it less than you intended for pixel work, if you're like me you'll discover a second usage by experimenting and having fun drawing with art programs which simulate watercolor, charcoal etc. This is very good for motivation (and possibly discover a new passion!)
Note that if you live in a high-population area, you may find a lot of used tablets in the classifieds (be sure to search for "GRAPHIC tablet" or "wacom", to filter out the ipads). Near me, I can see used entry-level Wacom tablets for 25$-50$. If you find one that looks physically in perfect condition (no scratches, stylus point doesn't look "used up"), it's good to go.