Just because a few people have successfully pushed their devices to 1000+ with these mods doesn't mean you will have similar success. Depending on how stable the components are on your gridseed, mods may even degrade performance.

As an example, the bridge mod is supposed to push the stable overclock from 850 to 950. I have two gridseeds running with just the bridge mod. One runs perfectly fine pushed to 1000 (1 or 2 HW errors per 24 hours). The other I can only push to 925 (any higher and I go from 0 HW errors to multiple HW errors per hour). The only difference is the 925 one came from a later batch.

EDIT: This is not to say that modding won't get you any benefits. In most cases, modding will allow you to get more hashing power. However if your expecting to order 10 gridseeds and mod them thinking you're going to get 1200 MHz out of each one then you may be in for some disappointment.