Excuse my ignorance --- it takes much longer time to mine one XDN, is it due to the hard fork?
Yes. The hardfork enabled merge mining, so now minergate is mining XDN with the entirety of their Monero hashrate, and probably collecting 99% of all XDN block rewards. Not sure how many Monero miners on minergate are requesting XDN or if it's automatically setup to reward them. There's no open source software for merge mining pools though, so I think at this point minergate just gets all the coins.
Yes, I think merged mining is working well for DigitalNote's security. Looking into
https://minergate.com/ I see their pool currently has about 20% of the hashrate with 847 miners in their pool when writing this. 520kH/s worldwide with 107kH/s coming from their pool. There is a lot of informative stats available on their homepage by following the above link.
Before the XDN fork I had only one I5 CPU dedicated to XDN. Now I have switched most of my mining rigs to merged mining between XMR/FCN and XMR/ FCN now helping to secure three coins with a bigger hashrate instead of two. Essentially. all of my GPUs have now doubled their hashrate.
I still would like to set up my own pool if I ever get a chance to learn how.