I did LEL in 2017 and PBP in 2015
I wont be doing PBP this year as I'm recovering from a serious arm injury and haven't been on a bike since February (and not likely to be capable of safely riding a bike for at least another two months).
I loved LEL. As Hank says it's mostly flatish (apart from the double crossing of Yadd Moss and some lumpy terrain around the Lincolnshire Wolds) and I'll never forget some pretty brutal headwinds on the return journey around the Cambridgeshire Fens.
The controls are nicely spaced at around the 100km mark and offered both great food plus warm & relatively comfortable sleeping options.
For PBP I did the SR qualifying rides (200, 300, 400 & 600km) but for LEL I was on a RRtY attempt so the longest I did was 400km).
For me the important things to consider are to get comfortable on the bike, make sure you can ride multiple long rides (I did a 200km ride one day before doing a 400km Audax over the next two days). Finding a group to ride with helps enormously, Oh and make sure you are happy and comfortable riding at night.
However THE most important element for me is what you head is doing. I think we all put too much emphasis on the physical aspect of doing long rides. Most folk people neglect the mental aspect and are often beaten before they set off.
Hank Chief nails it for me. Just get on your bike enjoy the ride, stop have some food and a wee stop, get back on your bike and repeat until you need a short sleep.
I looked on it a a series of relatively short and easy 100km rides punctuated with well run food/rests stops.
The controls were mostly decent, with plenty of food available (excluding Louth - which did experience problems).
As I'm not able to ride PBP this year I am definitely planning on doing LEL in 2021 and if any one is keen to hook up to share prep rides, travel or on-event support please give me a shout.
TMS