I have had both in the past. I had a double HackSack in my Scamp and a queen TravlSack in my TrailManor.
I found that the TravlSack was by far the best of the two unless HackSack has changed since I bought mine. The HackSack had just short strips of Velcro with gaps between and I was always getting a foot or elbow caught between strips. Also, it was very easy to pull the HackSack sheets loose from the sack. The TravlSack has continuous Velcro and stayed prioperly assembled.
My biggest complaint was that they were either too hot or too cold and I often had to pull the velcro apart to get comfortable. Also, since they were symmetrical, there was way too much bag up around my face, especially with the thick layer on top.
If I were to buy one again, I would buy the TravlSack. Fortunately, I now have a bed that can be made up with normal bedding and I am much happier with that than with either sleeping bag.
John W. Irwin
2005 Classic 28 "Sabre-Dog III"
2013 Silverado 2500HD Duramax/Allison LTZ
WBCCI #9632, TAC TX-10