Hi Fairuz,
I’m also trying to make resin spheres and I’m new at this too. I have molds very similar to both of the ones you linked to. I only tried using them once. For the first one, the hole on the top was too small for when I tried to pour the resin and it spilled over the sides. In retrospect I should have used some time of syringe or eye dropper with a small nozzle to fit within the top hole of the mold.
Since I didn’t successfully get the resin inside the mold, I never found out if there would be a line in the middle part. But if I had to guess it looked like the mold fit snuggly so I don’t think it’d leave a line.
The 2nd mold seems to have a wider opening to pour the resin in. Also, with this one you can use a rubber band to keep the mold tightly together so it wouldn’t show the line seam. The obvious con is that it’s $45.
I’d say try the cheaper one and see if it leaves a line. If it does you can try sanding it down.