While most locks are universal, some manufacturers have started to make and distribute models that work better with certain types of guitars. For instance, you can now find locks that are specifically made for bass guitars. The main difference between a model of this sort and one that is made for an acoustic instrument is the fact that it contains a larger guitar strap button, that is better suited to hold the weight of the instrument.
However, if you are not searching for a product that comes provided with very particular features, it is best that you simply look for a lock that has a design that you like and that is made of high-quality materials. If you have the time, you can also look at what other buyers had to say about it by browsing through the reviews that are available online. If you are part of a community, you can also look for recommendations from fellow players.