The original version of the N-Tester is no longer available.
The new model N-Tester BT is available FREE of charge when you create an Atfarm account.  Just make sure when you choose your plan you select an option that includes the N-Tester.
If you already have an Atfarm account you can upgrade your account to a plan that includes the N-Tester.
There are only a limited number of N-Tester BT devices available so if you are interested, make sure you are quick.