Update: see information in this reply regarding what the door manufacturer said about this - basically they can't get a barrel that fits any more, and it doesn't affect the gaurantee.
I had my locks changed today to deadlocks, to prevent my toddler escaping. I left a key for them to do the work, I wasn't here. Note that this is a PVC door with multipoint locking.
The replacement locks juts out about 10mm, whereas the previous one was recessed. This looks odd to me especially with different locks side by side. It looks to me to increase the risk of water getting into the door, rusting the components.
Does anyone know if this is good practice? I'm really interested in people who know what they're talking about here.
Note that to save $100 we had only one of the French door locks changed, because you have to open the main one before you can open the second door.
I called a locksmith who said they see it reasonably often, and that they'd avoid doing it, it could rust the workings eventually, but PVC doors can be tricky. So their opinion is it's not great, but it's not awful either.
Here's thumbnails for larger versions
Both locks
The new lock only
The old lock