While (as you know) my practical experience with PCP is fairly limited, I can offer some thoughts on the product when I considered it before taking out the BM agreement and SWMBO's skoda yeti agreement.
IMHO the main dis-advantage to PCP is that it
can put your supplying dealer at an advantage over you when it comes to the end of the agreement. Most manufacturers tend to be conservative when it comes to the Guaranteed Future Value (GFV) of the car, probably for two main reasons.
1. They wouldn't want you being able to walk away from a £10k car that you owe £15k on, which you could if they were too adventurous with the GFV.
2. By making sure there is a chunk of equity in the car, they have much greater power to keep you within their brand. Taking my BMW as an example, the GFV is £13k plus change. Looking at the classifieds, a 4yo sensibly specc'd M135i with under 50k on the clock cannot be had for under £18k private or £21k on BMW's approved used scheme. The problem is of course, selling a £20k car privately is no mean feat as you are open to a whole array of scammers and charlatans wanting to rip you off.
So, after my agreement is up, I'm faced with either taking out a personal loan to buy the car (not an option for a lot of people), trading it in as the deposit on a new model or walking away and "handing" the dealer my £5k of equity. Clearly, most people take the second option, hence "trapping you" in the brand.
Consequently I think its rather important to decide on your "out" for the agreement before you get into it. At the end of the two car agreements, SWMBO and I need to stump up £22k if we want to but the 2 cars, or walk away from the best part of £9k's worth of our hard earned. Needless to say we won't be taking the second option! But we need to plan ahead to make it all works out.
My other thought would be around interest, the Skoda pcp was a no-brainer at 0% - anyone would think they'd just been in the grip of a major PR disaster and were struggling to shift cars
. The BMW 5.9% may or may not be competitive depending on you circumstances, for us, it wasn't particularly competitive but I chose to take it as it simplified our finances rather than juggling a loan, 2nd mortgage and a PCP deal. It may be tempting to look at funding a car through other forms of lending, but my only concern here would be making sure the life of the loan and the projected ownership of the car match up. It would be sad indeed to still be paying a loan on the car after you no longer have it!
Sorry if the above musings are teaching everyone to suck eggs, but I thought they may be of use.