Connecting two scanners to a single antenna through a T will reduce the signal to each scanner by 1/2. All multiple port splitters require an active amplifier to compensate for the loss in the splitter.
I have used a T connector and it can work as long as you can live with some signal loss. It isn't a 50% signal loss but you will notice a difference in signal. I also tried using a amplified TV splitter with good results before I got a Stridsburg. Just food for thought.
People often try and use one antenna, but... I personally think you're better off with having individual setups. By the time you pay to do the split right, you're pretty close to paying the same. Plus, with multiples, it gives you options by having antennas that focus on different bands... ie: better overall performance. Unless you're just absolutely forced with having to use a single one.
I use a MCA204M by Stridsberg for up to 4 scanners with good results. One thing though that I have noticed is that the MCA204M may induce some noise that seems to somewhat negate the benefits of a splitter vs. just using a T connector with two scanners. I don't have the MCA204M grounded, and perhaps that is the reason for some noise.
If you're listening to fairly strong signals, then a 50% loss (3 db) may not be a big deal, and you can save some money with a T. But that's for two scanners. More than that, and the losses add up. Most folks I have contacted on this list who use multiple scanners generally seem to be using some type of splitter like those by Stridsberg. They seem to be well constructed. I actually have two of them.