Bullworker, the rest are fakes.
The product is much maligned. It was and still is a very effective fitness device. While the emphasis was always isometric... the Iso-Motion (Dynamic Tension) aspect is very effective. Furthermore, if one will apply "super-sets" to their use, they will be amazed at the increase in "strength" they will achieve. As for bulk increase... no. The Bullworker Arnold Challenge gave an exercise only power lifters who could bench 400 lbs could achieve. The new Classic has over 200 lbs of end resistance. The Steel-Bow can perform 100 lb resistance curls. No, it is not nor will it ever be free weights, but it is very effective when it is used properly. The Iso7x is a knock-off and there are plenty around trying to cash in on the Bullworker name. Side by side, it is obvious why they want to be like Bullworker... and are not.