They are the exact opposites! Lacrimosa is big, epic and loud, while Insolidus is silent, soft and lyrical! I wouldn't even think of it if I could afford it (what stops me is that I need to pay the extra 250 EUR to upgrade to Kontakt only to be able to use them).So Insolidus comes to $166 with the added discount. That's pretty good. Thinking about it, since I have Lacrimosa already...wanna make sure it's not redundant.
From all the videos or walkthroughs I have ever watched and the all sound demos I have ever heard, the combination of Insolidus + Lacrimosa is my dream combination, it can take you from the softer up to the louder part, together they can get you covered for any style you need.
If you want just take your time to explore "Insolidus vs Silka", because they are very similar (both soft). Still I would choose Insolidus (and one day I hope I can do it)!