We have a product called Timber Mate here in Australia, not sure if it's the same product though. The stuff I have used is water based, easy to apply if first thinned with water, fills reliably, stays in the grain, and sanding is a breeze. The label looks like this:
If you are going to try this product, I would recommend filling as required, sanding back, but not too far as you want the filler still above the pores for now and then leaving it to dry right out, (at least a couple of weeks in warm dry area would be best) then sand back to wood just before applying your finish. This is necessary to avoid the sink back you can get with water based fillers. I used this product on a resto around 12 month ago and no sink back as yet but you do need to sand it properly to get the colour out of the wood or it will look muddy, the catch 22 is that there is quite a fine line between not sanded enough, and sanded too much so it has re-exposed the pores.
Like any thing to do with the finishing process, the best advice is to pick what is best for you and preserver with it because they all work properly, when you do.
Cheers
Kim