Come on the poster is a commercial pilot in europe he is proberly going to be doing 40-120 sectors per month.
He wants to go fun flying while on holiday in the states.
He really doesn't want to let his proffessional log book go missing in action because its a whole heap of a PIA and looks a bit dodgy if he wants to apply for more jobs. (witterings by a CFI outstanding)
Having a separate small log book with everything in it to allow him to comply with FAA rules which doesn't really matter if it goes missing is by far the way forward. The ins and out of what he has done doesn't really matter because I presume that he only wants to go flying while on holiday and a FAA ppl is more than enough. If he wants to keep his SEP valid in the UK he can transfer the hours into his pro log book when he gets back home and use his LPC as his flight with an instructor. Its not as if he will be doing 50 hours of hour building when he is in the US.
A pro log book is a completely different beast to private in the grand scheme of things it can mean the difference of getting a job and not getting a job. If there is any hint of fiddling or issues and someone else will get chosen. Its a bit like the service history on a car.