The Xtunes are pretty nice rams using AeNeon's own chips.
These rams will run at it's stock settings stabily with no concerns.

However, the downside comes when we take Overclocking into consideration.
The DDR2 800 Xtune and the DDR2 1066 Xtune kits will not overclock well regardless of the amount of voltage pumped.

The DDR2 1066 kit will max out around DDR2 1100 iirc.