I've never heard of a sauna suite, but I assume that you mean something that causes you to sweat while working out. Yes, they work, if all you've interested in is sweating. However, they will reduce your exercise tolerance thereby reducing you ability to become fit.
The purpose of exercise isn't to cause sweating. One cannot gauge the effectiveness of exercising by the amount that one sweats. In cool weather, you might not sweat at all but yet your exercising might still be very effective. And, in cool weather, you will be able to exercise more because you will be less likely to become dehydrated and over-heated.
Take, for example, running for exercise. If you wear a sauna suite, you will overheat quickly and not be able to run as far or as fast. Thus, your ability to exercise will be reduced and you will not become as fit. Also, if you are trying to lose weight, you will lose less weight because you won't be able to exercise as much. The weight you will lose while exercising will be water because of the sweating and that must be made up by drinking more water else you will become dehydrated.
You lose weight by eating few calories than you burn. Thus, exercising more will cause you to burn more calories and the more calories you burn, the more weight you will lose. Losing weight through sweating is very temporary.
The only justification I can see for a sauna suit is if you have to do running workouts in cold weather to prepare for a race which will take place where the weather is hot.