I've done a number of complete leather seat re-covers and found that hog ring pliers are essential. Essentail for a nice finish. The ones I have were fairly cheap - $15.00 from a Home Hardware. In some cases the hagring pliers were the best tool to use when going through a thick amount of sponge and a guidewire. I also use tie straps on occasion when I have 2 finishing ends that need to marry up with each other and need to be stretched. Any time I find that I need to stretch any of the leather I'll use the tie strap first and wait a day or 2 and then replace that tie strap with a regular hogring. Tie straps can look unsightly if they're used in certain areas that can be exposed.
1990 JDM RHD - Stage X 491.0 RWHP, 476.1 RWTQ, 18 PSI, Pump gas 26PSI w/Race gas = ???