Considering that they all end their prayers with something like : "We send this prayer through Jesus, Aman", I actually don't see anything wrong with their teaching.
That is a fair and balance statement to make.
a name made up in the 12th century. The name Jehovah isn't God's name
This statement however is unfounded. The only argument I would make about that being God's name is that there is no V in it. It should be spelled Jehoah.
To believe that that name was made up in the 12th century would mean that every Hebrew name that contains the יהוה (YHVH) as either with the prefix יהו (YHV) or the suffix יה (YH) was also made up then too.
Yes it is true the over time Y's were changed to J's and I's but that doesn't change the basis for the the vowels used in these names and how they would be spoken in today's English.
These names were never stopped being pronounced and replaced with LORD (adon).