Mouse,
Your questions about the tight beam, it does require a more precise alignment. This also means a more focused light that would be more tolerant to snow but less tolerant to vibrations. I have both tag and alge cells that I use regularly and find them both fairly equal with regards to performance. As mentioned before I use through beams for all USSA/FIS racing and rarely get a false finish for snow. I do see TAG reflector setups used regularly as I manage the NASTAR venue at the resort where I live and when it snows hard, we get false finishes, even with a finish width of only 12 meters. We had the old ALGE units that you speak of about 20 years ago but I do not recall their performance in snow.
Really there is not much to understand about photocells, use through beams with good brackets on solid posts (notched of course), align them well and check them between runs. If you are doing sanctioned races with two sets use the sync cable with the PR1a or HL-232 to prevent bleed from causing problems. If you do not want to spend the money for through beams have a good timer who is paying attention and sync your had watches so you can easily identify a correct impulse in blowing snow. Keeping the finish line narrower (within rule limits) helps too.