I'll preface this by saying I've never used a SCR, but I'm a CCR diver.
Deciding to move over to the rebreather world being semi closed or closed circuit is a very big choice. It's not something to just go into it thinking it's something cool or neat to do. A rebreather is a piece of gear that can and will kill you if you make even the slightest mistake. You really have to look why you want to use one, and what you will be doing with it. It takes a lot of discipline to dive the them. With both units, you just can't throw it together and get in the water like you can with a scuba setup. If you make a mistake in rushing to put it together and fail to doing it properly, a whole host of bad things can happen. And many of those problems will kill you. You have to have dive buddies who understand what you are doing. Most other divers who are Open circuit divers, don't want to dive with me anymore for the most part. I take longer on the surface getting ready with my pre-dive checks, and in the water checks. If you're diving the SCR to get longer bottom time or getting closer to fishes, you're buddy will need to be on the SCR or CCR unit also. You will still be limited by dive buddies if they are on Open circuit still. With the SCR and what I have read about them, look at your dives and decide if you can do the same dives with a cylinder of Nitrox. Also if you're going to just dive solo with the unit, don't. If you have a CO2 hit or low Oxygen, those can put you out without you even knowing it. With no one their to help you, you are dead. At least with a aware buddy they can attempt to rescue you.
Decide if the unit is something you really want to do. It will probably cost you couple thousand dollars to buy one, then the yearly costs will probably be in the hundreds to keep the unit going. Training probably between 400-800 dollars depending on where you're able to find an instructor. My best advice is, look at why you want to buy one, if you'll have the dive buddies that will be understanding of it, and if the dives you want to do would be safer and more affective using open circuit. Also if you are looking on ebay for one, be very very very careful. Many of the sales of rebreathers on ebay are scams. Good luck with your choice.