I have both products. I purchased the Parliant solution about 2 months ago. I can't get it to work with the CID from my phone company (I have number only). Parliant worked with me for a long while on this issue but in the end they basically stated that their hardware was not capable of decoding my CID.
So then I purchased Ovolabs product....though the software is much less developed, I believe in the long run Ovolabs product will be a much better solution. I do have problems with this product as well, but the developer is very responsive to problems and getting problems fixed.
The support from both companies is excellent, but at the end of the day I would go with the Ovolabs product, mostly for the message recording feature. Also the developer of the Ovolabs product is a long time Mac programmer.
Hope this helps.
Dale