OP as previously said, Locker's is a lovely school, it has a good reputation locally, good facilities and very nice grounds. Nevertheless, please consider the type of senior school you may prefer for your ds in future as according to Locker's park website and local knowledge they do NOT send boys to the high flying senior schools regularly. Please see their Leavers destination list for past records.
If I were thinking of sending ds to the likes of Eton, Winchester et al I would be looking at a prep school that will give him the best chance, a prep with tons of experience sending lots of boys yearly, not the odd bright spark every 2 or 3 years. Eton makes no special mention of them!
However, if you are not looking at top public schools, Lockers is more than capable of getting children into good schools but much less selective as shown on their leavers list.
The boys are very very pleasant, and very outdoorsy, their sport is also quite good, if ds is very sporty he will enjoy it. I hear their food is also 'top notch' according to reports from after matches.