I am building a kid's rifle right now with parts I purchased from Sitting Fox (with the exception of the barrel). At the same time, I am building another rifle with a kit from Track of the Wolf. There is a definite difference in the quality of the parts, but there is also a price difference.
The TOTW kit had a brass cast sideplate, whereas the SF kit has a stamped piece that is thinner. The TOTW thimbles had mouldings and were soldered at the tab, ready to inlet. The SF kit's thimbles were unsoldered, formed sheet brass without mouldings. These differences will not make much difference in the finished product, but will require a bit of extra work.
However, the stock I got from SF has big streaks of greenish grey heartwood in it
and the ramrod hole is not drilled, but rather routed down from the barrel channel. This takes away a lot of wood that would otherwise strengthen this area. I also bought new screws for the kit, as it came with a wood screw for the tang rather than a bolt to engage the trigger plate and I disliked the other screws in the kit in general.
However, the SF kit had the lock and barrel pre-inlet and the stock had even been cut the trigger pull I specified with the buttplate mostly inlet. The triggerguard and buttplate were of great quality, as was the small Siler lock in the kit.
Overall, I was not terribly dissatisfied, as the kit was very inexpensive! Just know that saving money may mean cutting a few corners.