The Helsinki is the more compact variant out of the two and is a good fit to use in your day to day, for instance in the city, for work or university. It has a volume of 17L and two laptop pockets with the following measurements (Outer laptop pocket : 38 x 25 cm, Inner laptop pocket : 41 x 25 x 2 cm (for example: 15,6'', 16'' MacBook).
The Helsinki Pro is in contrast the larger and move refined version. It offers more storage space und is therefore more fitting when one intends to carry more or use the backpack for longer days at work, or short trips. It has a volume of 23L and a laptop pocket with the following measurements: 43 x 29 cm ( for example fitting for a 15,6'', 16'' MacBook).
To summarize: The Helsinki is ideal for a minimalist day-to-day use, while the Helsinki Pro offers more storage space and comfort and practical extras for a more demanding intended usage.