I teach classes once or twice a month to a variety of different age groups and while the venue is around 20-30 people what I have to speak about no matter how I project my voice just isn't heard. That could be from people talking in front of other people or just from general hearing difficulties. The numbers I speak need to be written down and referred to and while I do try to write on a whiteboard most people want to take notes. I tried using this in my last class and instead of putting it in front of me I put the unit in the back of the classroom with the volume a little lower so I could reduce my speaking voice allowing me to present longer without having to take a break and the people sitting in the back could still hear me just fine. It also kept from me hearing feedback of my own voice.The SAINTLARK S4 can be used in several ways:* Voice amplifier with a wired or wireless headset (both are included)* Mp3 player via USB drive or TransFlash drive* Bluetooth speaker* Auxiliary speakerThe first is most likely the reason you want this in the first place and the rest are just nice extras. There are two headsets included with the amplifier. The first is wired and plugs into the back of the unit labeled Mic. Straight forward and you don't need to charge it as long as the amplifier is charged. The second is wireless and can transmit on both Bluetooth and UHF. The headset charges in a few hours and pairing to the amplifier is done with the M button on both the headset and amplifier. Since I had this in the back of the room about 20+ feet away I had to use the wireless. I tried both Bluetooth and UHF and they both worked well but depending on where you use this there may be restrictions so having it transmit on either frequency is a plus.The second use is as an Mp3 player that you can plug in a USB or TransFlash card and it auto plays the first song in the list and you can track jump forward and back as well as fast forward and rewind in time blocks. As there was no specifications listed as to the formatting of the drive I tried the big three. FAT32, exFAT, and NTFS with the first two recognized and NTFS unsupported. I used my USB-A 2.0 32GB drive. It will not accept using the USB-C port as an input.The third use is as a Bluetooth speaker version 5.0 and will show up as S4 on your phone or other devices like a laptop. This is very helpful if you need to play a video during a presentation and need the audio to reach the back as well. I found that using the headset on UHF and my laptop transmitting on Bluetooth it was easier to transition back and forth with the audio.Lastly it can be used as an auxiliary speaker to plug directly into with the provided 3.5mm cable.You can also plug in your own microphone into the 3.5mm port separate from the AUX port if you prefer to use one you already own. Sadly while you can transmit audio playing from your phone via Bluetooth you are unable to wear your own Bluetooth phone earbud as the mic and I tried.The unit also comes with a hand strap to just carry or an adjustable strap you can hang over your shoulder if you need to be on the move if you do tours for groups or something similar. There can be some feedback so you will need to find that position most optimal to prevent it or adjust the echo. It's just easy to ask everyone if they can hear you clearly and adjust if necessary. A split USB-C/USB-A/USB-C cable is included but just listed as a charging cable. This allows you to put the USB-A into a charging block and simultaneously charge both the wireless headset and the amplifier itself. That was a nice touch to include in the package. There is no case so you will need to store it in the box but the box does have a handle if you don't want to purchase a separate case for it. Overall I'm really pleased with the design and what it can do and I'm sure other people will have all kinds of specific uses for it. It certainly has made my presentations easier and clearly understood so for me it's a recommended purchase.