Jaroslaw
At this point for use with SCS900 and Siteworks I would still recommend that you use the SCS Data Manager to do this kind of conversion - if you have a LandXML that contains an Alignment and a Surface, SCS Data Manager has the original File Flipper and that converts LandXML to PRO no problem, it also organizes it into the correct folders for Sites, Designs and Work Orders as required for SCS900 / Siteworks.
SCS Data Manager was written for the Field SPS products whereas File Flipper and Works Manager have been written more for the machines and they really don't support the SPS systems that well when it comes to Roads.
As a user - I would personally always use TBC - appreciate that maybe the customer is reluctant to do so, but it is so much easier to load the data and preview it and then push it out to whichever systems that need it. If you import a LandXML file with an alignment and a surface in it, you can make a corridor using the alignment and use one instruction - a surface instruction to add the imported road surface to it to make it into a corridor. You can then export to SCS900 as a PRO or SIteworks as a VCL or PRO or to GCS900 / Exarthworks as as SVD/SVL or DSZ in one pass.
You do not however need to create a Corridor to export an Alignment and a surface as a PRO file - you can simply select the alignment and surface and output it as a Road Surface model and that works well also.
The challenge with Flippers is that you have to know what is in the source file and how that will be converted to the PRO and also you have to 100% trust that the data in the source file is good - if you bring it through TBC you have validation tools to make sure that is the case and you 100% know what you are working with and that when you output the data it will be 100% what you need for the field system.
The Field Data Edition of TBC is a good start point, but if you want to go down the Flipper route I would use SCS Data Manager to create the data for those devices and then load it into Works Manager as required.
Alan