Yes, the down time is a problem and customs can be a pain if the paper work is incorrect.
If you want to use this shop and if you can live with the down time in case of a problem I would recommend them. I had bad luck and I might have suffered financially but they were honest and did not muck me arround. If I will ever have to o/h another engine I will think very hard where to send it but they will be one of the options.
Either P.M me your email and I will send you something to read or let me know when you are next at Elstree and I will try to meet you.