Have been to kiss for a 90 minute 50/50 massage tantric + b2b with Ruby and Bella and found it excellent. Similar to Tantric Massage London in that the set up feels relatively professional and high production value (compared to others) but different in that it's slightly more raunchy and you feel the girls at Kiss are putting on more of an act to please you. I'm not the type to push the boundaries with touching the masseuses, initiating un-advertised extras etc so I can't comment on that.
Other 4-hand options would include Maya of Hammersmith's outfit:http://london.backpage.com/BodyRubs/new-pictures-body-to-body-and-tantric-massage-by-european-ladies/12205165
and Gina's place in Romford: http://romfordmassage.co.uk/therapists.html
Gina is reviewed here: https://www.ukpunting.com/index.php?topic=69209.25
At Gina's the 4-hander was more mechanical but Gina and the girl she was working with were extremely hot so it was still quite a fun experience.
At Maya's I would say the experience varies depending on the experience level and comfort level of the girls. If they are used to working together then i'd say it's not an issue but sometimes I find them to be a tad shy/awkward which of course effects the experience.
If anyone has more recommendations I'd be keen to hear them, and to hear back from the OP about his experiences in this field.
On the whole I tend to prefer 4 handers performed on a bed because there is more space for horizontal touch and interaction and it feels less formal.