If you are looking to use it for work, its a handy machine to have on any farm, but you should beware of some things like assessing undercarriage wear accurately by measuring, so you know what you are dealing with there, its an expensive part of a crawler to rebuild/replace.
Ideally, its just better to spend a little more or significantly more if in the budget for one that is field ready and checks out to be in sound mechanical condition.
Its nice to own, as its there when you need it, but also cost effective to rent for larger jobs, or for the improvements you want to make.
Theres more to it when looking at used crawlers, also parts support and so on, many are used and abused, others not, you need to really have an eye for what to look for on various MFR's and models, find one you think is a good candidate, have an experienced hand check it out for you, can be a big money pit to repair if you are not all that careful, nice new shiny paint on an old crawler with worn out tracks and other hidden problems has fooled many a buyer. And of course you never know, you may find something decent, older, worn but plenty of life for limited use on a farm or occasion.