The heads are the same, but the HD will have more weight on the side of the head, so likely that will feel more aggressive. They are both gentle smooth shavers though.
Merkur fixed-headed razors are all the same and quite aggressive. My first DE was the LH Classic and while it's my favorite now I loathed it when I got it. It wasn't until I got my next razor - a Tech - that I began to enjoy DE shaving and get the hang of it. After that, I could use anything.
I started with a Merkur HD, and it is aggressive. But then I switched to a slim adjustable and it is much better on me - much less nicking... With the Merkur I used my styptic nearly daily, now only once in a while.