I learned at EFT in Florida. Great experience and got the PPL cracked out in under 21 days. I wanted to do it quickly and I saved over £2k in the process. Granted this was in 2009 though....
Your nephew has to do what is right for him and there is nothing wrong with doing the PPL in a short period of time. It's cheaper as you don't spend the first half of the lesson relearning most of your last lesson due to the weather being poor and causing delays and gaps in your schedule. My only bit of advice is, keep your flying regular and consistent when you return otherwise you will fly daily and then come back to a flight once a month like I did. Not a bad thing but you need to ensure that the license can be kept current taking into consideration fitting in flying with your daily work routine etc.
The weather argument is invalid. As a previous poster stated, I learned more about proper weather briefing over there than some of my flying friends learned over here. You need to bear in mind that storms can appear in no time in the states so you need to learn to recognise the signs of build up. I flew a little close to a storm and learned how severe the weather can be the hard way...!
Bad points about flying in the US (Ive mentioned them in past posts and been shot down for it) the R/T, in my experience, is not as professional over there in comparison to the UK/Europe. Away from the large airports (Orlando, Miami etc) there are very few areas of controlled airspace. Both are minor points as long as you come back and fully familiarise yourselves with your local airspace to avoid any potential infringements upon your return.
Re the FAA to EASA conversion, find an EASA registered school and you get a european license... problem solved.
Paperwork is a lengthy process but not difficult as long as you have nothing to hide....!