How good a substitute is callaloo for spinach? I have seen some good recipes using spinach and have heard over and over that callaloo (amaranth) can be used in place of it.

There is confusion about callaloo the plant and callaloo the dish I am refering to the plant amaranth. 

I have never tasted spinach and I can not get it to buy where I am from, callaloo is easy to come by, I am hoping that someone here who have tasted both can tell me if this is true that callaloo can be used as a substitute for spinach. If i can get an answer here it would be a bit better than experimenting.

I have seen some substitutes for spinach on the Internet but unfortunately all fall in the hard to get category for me.
I've only had red amaranth, so apologies if that is distinct from the type you have access to. As I recall, spinach is a bit sweeter and the leaves are a bit softer so they break down more readily. Also I believe the stem on spinach is less fibrous.

That said, they are both leafy greens and I've yet to find a recipe so touchy that one leafy green can't be substituted for another.