I've used Orange Seal for the last 3 years.
Originally butyl tubes, latex the last 60 miles.
Discovered tubulars 3 years back and I've had 3 flats since then:
1) Didn't know about sealant, 1oz in each tyre fixed it
2 + 3) Apparently you need to top up, 1oz lasted a year.
So basically no flats...