Yes you can put it in your sump. I dont have a sump so i just put it in my Fluval and my Aquaclear. I just put it with the media. The good thing about it is that you can regenerate it. I really like it and i would recommend it. Anything else you want to know about it, feel free to ask.
its not expensive when you regenerate it. Your lazyness was just making it expensive hihi. Purigen is a synthetic absorbent that removes a wide variety of pollutants, proteins, ammonia, nitrites and nitrates, with practically no impact on trace elements. Purifies aquarium water, raises redox levels. I would recommend it and i always use it. A 250ml sells for about 12 bucks and it could last you for years depending on the size of tank. The option is up to you. but i recommend it.
It's a good ion exchange resin that complements carbon quite well. It does change color as it becomes exhausted, so you know when to change it.
I do use it and find my clarity is a bit better when in use, and I really view it as a stopgap measure to control excessive nitrates. It is not, however, as efficient as skimming and water changes, so I would not expect miracles.
I use it. I like the fact that it changes colors when its done and you can regenerate it. Mine seem to get exhausted about once a month but to be honest I don't know how much it is doing for my tank. I put them in my sump. As long as they are changing color I feel like it must be removing some bad stuff out of my tank so I will continue to use them since there doesn't seem to be a downside to using them.