The Rockrider 5.29 is now 5.1 BIG 29", and the first comments are good.

Finally the Rockrider 5.29 is available in all Decathlon stores, a friend of mine said there are a few also in Decathlon near where I live so probably tomorrow I'll make a visit.
There is some mess with the name of the bike: in Italy it's called RR 5.1 BIG 29" (link), qualifying it as the 29" version of the Rockrider 5.1 (exactly like the BIG RR 5.3 is the 29" version of the 5.3) as you can see here, in Spain, Germany and UK it's called just Rockrider 5.29 as you can see here, here and here, in France simply 29 pouces 5.1 as you can see here.
Just to add some confusion, in the BTwin website the same bike is presented as the Rockrider 5.3 BIG as you can see here, but I suppose it's a mistake.
Ok, this thing of the different names is not important as long they made clear that it's the 29" version of the 5.1 and not of the 5.2.
It's way more important what you can read in the comments section of the french and of the italian page. A good 90% of the customers are more than satisfied with this bike. That's good!