I think either will be fine -- your sticking with what you have (you're the mom/teacher, after all) or selling and changing like Stephanie mentioned.
For myself, I admit I'm strongly biased towards Singapore. It's not a matter of being "advanced" in terms of doing multiplication early. It's a matter of learning to "think math" rather than plug-n-chug like most American math programs (I haven't used Horizons but assume it's a typical American method). I like getting in the Singapore lessons for sure, and then kids can do all kinds of other math things as extras. My youngest used to do Math-U-See as an extra when he wanted to hover for a while in math, and we had lots of other math materials around here. I know it's an expense, but sometimes it can even be a gift at Christmas-time or something. Or there is resale, as Stephanie mentioned.
My grandson does his public school math, including the math enrichment class there, plus he does MFW-1st math as an activity with me sometimes, but he also wanted more math workbooks last birthday/Christmas. I took him over to the teacher supply store and he chose a big, fat one for me to give to him. He does that in the car or during long church sermons (maybe I shouldn't admit that
) or just when he wants something to do. He loves it when he comes to something new and I explain it to him. I don't necessarily think he gets more than a surface understanding when I tell him how to do "hard stuff," and I hope to be able to teach him deeper understanding using Singapore next year, but he stays excited this way and has plenty of confidence. We also do a lot of math via board games -- he likes to make them up and he likes to get thousands of points LOL.
Well, I've digressed pretty far by now from helping you make a choice, but just wanted to add there are different options for blending things, as well, including gift-giving. We like math at my house
Julie, married 29 yrs, finding our way without Shane
Reid (21) college student; used MFW 3rd-12th grades (2004-2014)
Alexandra (29) mother; hs from 10th grade (2002)
Travis (32) engineer; never hs