After using Toppik for a while, I ordered Dermatch last week and it arrived today.

I just applied it. Wow, this stuff is good! Really thickens the hair and is not as messy as Toppik. I liked Toppik, too, but Dermatch seems like really a good deal. The color is a match and the results are great.

How would you compare the qualities of the two? How do they differ?

Toppik is very light and it doesn't feel like you have anything in your hair. It's harder to get decent coverage with less hair. This actually holds true for all concealers but Toppik is the hardest out of the ones that I've tried. It works great for giving HT's the look of a little more density. It comes off w/ water.
Dermatch can fill in the gaps like you would not believe. It makes my hair look chalky unless I wet my hair again and towel dry it, taking off the excess. (thanks Dart) This stuff will stay on in water, sweat ,etc. It is "heavier" on the hair and has a strange kind of waxy feel to it. It also takes a little longer to apply.
Pro Thick is a spray on. Surprisingly, it works well also. It's much faster to apply than Dermatch but it can be a bit messy in the bathroom. I would think it would be harder to apply on the hairline, being an aerosol. I think it stays on in water also, but I haven't really tested it like I did Dermatch.
I usually use Dermatch first, then wet again and towel dry. Then I use Pro Thick on my crown on the spots where I don't have much hair and the Dermatch won't stick. It works. Maybe a little hairspray add some shine after that.

What is better, in your opinion, at concealing the hairline? I am 6 months into my HT, I still have some growing to do, so i would like to conceal the areas of my hairline that still have the appearance of thinning.

Do you guys recommend Dermatch, Toppik,or Prothik, etc?

I'm guessing that Dermatch would be your best bet. I say that because it's really easy to apply at the hairline and fade it to give a shadow effect.

I've been using Toppik for the past year or so, and it works great. Looks natural and no one would be able to tell the difference. The only problem is that it's not waterproof or more importantly sweat proof. Hence I've had to put my physical life on hold. I heard good things about Dermatch and was pumped cause finally I figured I could get back into sports. I bought some and it looks okay. My main problem is that it goes red on me. Yeah, it does the chalky thing too. But as previously stated, I just wet it again and it goes away. It's just the red does not work. Really disappointed cause it's very durable and WAY cheaper than Toppik. If anyone knows how to get rid of the redness, I'd appreciate it.

danger

Redness? I'm not sure I know what you're talking about. What color is your hair and what color Dermatch did you order? I use a combination of light brown and blonde for my hair. Maybe you need to mix to get your color right.

yeah, I hadn't really heard of anyone else getting it either. My hair is a medium brown, and I use medium brown. But yeah, the red is just not working for me.

danger

danger,
You could probably email them and ask about it. Maybe you got a bad batch or maybe you need a lighter color.

I was about to say the same thing. I think it may be that you need a lighter color also.