Sorry for the late reply, I dealt with 9ff a couple years ago but rather business related than as a customer so things might have changed since then. Jan Fatthauer is a cool guy, pretty laid back. I´d say that his company is basically a one-man show and follows a hands-on approach. Therefore most developments are pretty individual and different to companies like Techart where I believe that one single tuning configuration is being developed, tested and offered as a single product. 9ff, and I believe RS-Tuning as well, serve individual requests much more.
Therefore, if you are only looking for a tuning in the region of 700 hp, most other companies can offer the same. If you are seriously aiming for four-digit hp numbers there won't be many other companies around offering a similar product.
That said, which car do you base the tuning on? For a long time, these numbers were only achieved with the old Mezger engine as a base, I have no knowledge how good and reliable the modifications are on the newer engine generations although I figured that 9ff offers these as well by now.