I flew this the other day. There were at least two other people who I saw on the DPS-MNL who joined me on the MNL-LHR. Presumably they also had grabbed the mistake fare since otherwise the route isn't all that convenient.

The overnight flight from DPS-MNL is excruciating. Limited recline seats, etc. Dinner/drinks are served, rather than just turning off the lights and letting people try to get a bit of sleep. Also, the lounge at DPS is jam-packed with Jetstar and Qatar passengers at that time of night. Transfer at MNL is reasonably efficient, although the airport isn't very modern. The hardest part was probably waiting 7 hours in MNL in the lounge, which doesn't have particularly comfortable seating or decent food. In hindsight I should have booked the nearby Hyatt or Conrad to get a few hours sleep. Probably worth "wasting" some hotel points, considering the cheap flight.

The flight to LHR is fine. As mentioned, these are old Iberia A343 planes and the set up/colour scheme, etc. is completed unchanged from their Iberia days. The seats are angled lie-flat, but at least you have lots of space (other carriers have your lower legs in a coffin under the seat in front) F&B / service is good - nothing special but perfectly fine for a business class product. Nobody is hovering over you or asking you frequently if you'd like anything, but if you call for an attendant, they're happy to serve you whatever you like.

Still waiting for my ANA miles to post...

Of course the fare was great, but the itinerary is much harder on your body system than just catching a flight up to SIN, KUL, BKK or HKG and using miles for a proper flat bed to LHR...