I used that Nikwax and chucked it in the garbage.
Have used Sno-seal for years and can't say I've had any issues with leather weakening or being adversely affected especially since my go to hunting boots are over 15 years old. They are worn to hell but still waterproof. The soles are awfully thin though and I've sno-sealed them since I got them.
edit- this thread got me to order some Obenaufs. They had some special deal that had their leather oil, protector and some silicone stuff so I got it. I've got some expensive leather furniture that has needed some sort of treatment, especially a leather chair/ottoman but I've been afraid of screwing it up with something else. My oldest boots were dried out and I was going toput sno-seal on them but did the leather oil as a test and I have to say I was amazed. Leather feels like new. soft, supple and resists snow. Did the chair and at first i freaked because it darkened so much but after a day I'm amazed again.
The real kicker is my Rawlings brief case (baseball glove leather) that has sit in the sun on the passenger seat of my car for 15 years. One side is bleached out, dry, stiff and the other not much better. Leather oiled it and almost like new. What's wierd is the Obenauf's make the leather smell like new rather than smell like the oil/conditioner. etc.
I'm really impressed. going to hit my good boots with the LP before I go to the Packers - bears game Sunday. bears fans like to throw beer when they lose so my boots had better be waterproof!