So, should you buy lifting straps or lifting bars? Well, that is a good question. It comes down to your gym's budget and what exactly you are looking for when it comes to workout equipment. If your budget allows, then by all means, get both!
The main reason that you should buy lifting straps/weight sets instead of lifting bars or dumbbells is because they allow for more flexibility of exercises. Dumbbells are very restricted in terms of exercise options. When you use a weight set, you can perform a wide range of exercises including squats, bench presses, overhead press, military press, etc. With dumbbells, you generally only have a single option of weight: the weight that it can handle for that particular exercise. With lifting straps/weight sets, you can perform a pretty much unlimited number of exercises - an almost unlimited number if you like!
Another major plus of lifting straps/weight sets is that they tend to be much cheaper than dumbbells, even when you factor in shipping and handling costs. Most people don't think to buy lifting straps/weight sets online; however, you can find some pretty great deals at your local gym. I actually got a dumbbell set with a full length mirror for less than $20 US and I'd highly recommend it! View here for more info about the best lifting straps.
If you don't have access to a gym, then I'd highly suggest you invest in some heavy weights and a pair of dumbbells. Start out with lighter weights and a few sets under par and then once you get the hang of it, you can move on to the heavier weights and higher reps. I personally recommend you go with a heavier set over time and then switch back to a lighter one once you're starting to see some results. Once again, I'm not saying that you should never use free weights when exercising, but I definitely suggest you learn how to properly use heavy weights before you start out. If you don't know how to properly lift heavy weights, then you'll end up injured and unable to do any sort of workout because you can't fully control your body.
The final piece of equipment that I'd like to discuss is the single loop arm strap. Now, you might not be familiar with these type of weightlifting straps, but these are used in different workout routines and are generally used by more advanced lifters. The big difference between these straps and the traditional ones is that the one loop arm strap (the ones you see most often) are built in and are attached to the bar with a single line - there's no hanging the weight from the side! The single loop arm straps are usually the heaviest, but they're also the safest because you have full access to them at all times.
As you can see, there are many different pieces of equipment that you can use to help you build up a muscle and tone your body. When looking for a way to improve your workout routine and add more muscle mass, deadlifts and squats are generally the best ways to go. They're the heaviest workouts, but they'll build the biggest muscles and they'll be safe (especially if you buy the right type of straps). The bottom line is that you need to determine what your goals are and buy the equipment that'll help you reach those goals. Take some time and really think about what your needs are so you can choose the best equipment for you! To get a detailed overview of this topic, see here: https://en.wikipedia.org/wiki/Weight_training.