The biggest problem with the OD (apart from the weather), is the lack of B&B accommodation on the route. Apart from small sections (Chepstow to Monmouth for example), there are long swathes where is nothing available (not even YHs), unless you are prepared to divert several miles to find somewhere. This can add several miles (and days) to your agenda. The OD is not a good LDP to do in one go, best done in small sections over a period of time