Hi,
I had a very different and positive experience with Ann Dobson, she cut my second son's tie quickly and minimised the impact on him and I as much as is possible, helped me to get him latched and followed up with phone/text advice and support.
http://www.ann-dobson.co.uk/tongue-tie-london.html
In comparison I took number 1 son to a specialist at Parkside who was useless and then to the Dragon Centre at St. George's who only did a partial cut leaving my boobs in tatters as a result.
I have to say that holding your baby while it's done feels pretty brutal and takes it out of you a bit so might be best to enlist the help of a granny or husband for that bit but the results totally justified having it done. PM me if you want to talk more.