An atty and a drip tip is the best way to test juices. I don't recommend using cartos bc then if you dont like a
juice you basically waste a carto. With direct dripping on an atty, you can just take a few hits, and if you don't like a juice, blow out the atty real well and put in another juice. Some flavors can linger in an atty, but with most after a round or 2 dripping a different juice, the flavor of the first juice will go away.
Be VERY careful with an auto battery though. With attys or carto, if you flood it and juice leaks out, you can kill the auto battery. That's why most people prefer manual batteries bc their sealed so they can survive juice leaks alit better, and manual batteries allow you to control your vape alot more.
If you start making your own juice, make sure you FULLY know what your doing first. DIY is a lot of fun, but can be dangerous if you don't know what your doing. Nicotine liquid is no joke, and needs to be handled and used correctly. Just getting some on your hands can make you sick bc it absorbs thru your skin. Download a good juice calculator and make sure you always check your inputs to make sure they are correct before you make a juice. Read the DIY stickies and as ANY questions you have BEFORE you start, no matter how dumb you think the question might be. I also recommend using syringes for your measurements of each component, especially the nicotine. Dropper bottles are not very accurate, and with nicotine liquid, you NEED to be accurate. Depending on how concentrated the nicotine liquid is that you get, putting even alittle more than your supposed to/thought you did can give you a juice with a much higher nicotine content then you wanted and that can make you sick, and even potentially be deadly. So just remember to use caution and educate yourself first and you should have no problems.
Goodluck with it!