I have a VIOOH, a Light Lens Lab copy of the Leica SBLOO (35mm brightline), a Leica SBOOI (50mm brightline), a Leica SGVOO (90mm brightline), and a Leica SHOOC (135mm brightline). I also have a Cosina Voigtlander 21/25mm brightline finder. Here are my thoughts on them:
• The VIOOH is great for 35mm and 50mm lenses. For 90 and (especially) 135mm, its nearly unusable because the image in the finder is so tiny. The VIOOH works by cropping the view to match the lens focal length. The 35mm view is big, and the 50mm view is big enough, but the longer focal lengths are too small to accurately compose in my experience. The VIOOH has a parallax adjustment that is quite accurate. Because 35mm and 50mm are my most-used lenses on my screwmount Leicas, it is usually in the shoe of my IIIf Red Dial.
• Light Lens Lab SBLOO Copy (35mm): I have never used the original Leica version to compare it with, but I don't really like it. The framelines are hard to see all at once, and are not as bright as on the Leica and Cosina Voigtlander brightline finders. There's a dashed line that indicates parallax at close focus.
• Leica SBOOI (50mm): Bright, easy to see framelines, nice finder. Parallax at close focus is indicated by a dashed line.
• Leica SGVOO (90mm) and SHOOC (135mm) these look externally identical; the large black side is actually the side you put your eye to, which confuses some. The framelines are large and there are two sets of framelines, one for infinity and one for close focus. These are not for parallax; they're because the image area becomes smaller at close focus! Parallax correction is done by turning a knurled ring to the focused distance, which is more accurate than the dashed line across the top of the image area used by the 35mm and 50mm brightline finders and similar to the system used on the VIOOH.
My recommendations: If you shoot with 90mm or 135mm, get the brightline finders for those lenses. If you shoot 35mm only, I actually like the VIOOH better than the 35mm brightline finder I have. If you shoot 50mm only, get the 50mm brightline, and if you shoot both 35 and 50, get the VIOOH.