The Allpa 42L belongs in the main-luggage discussion. If your ordinary load already fits comfortably into a smaller pack, moving to this listed capacity needs a reason beyond having room just in case.
Identify the item that needs more space
A second pair of shoes, bulkier clothing or specialist equipment can create a legitimate need for a larger bag. Lay out that item with the normal packing list and examine whether more capacity is the simplest answer.
If the problem is loose organization or an oversized toiletry kit, a larger backpack may preserve the same issue at a different scale. The 42L should solve a volume constraint you can describe, not replace the process of deciding what belongs on the trip.
Compare the exact Allpa version
This listing identifies Blue Spruce and Abyss. Allpa family information from a different generation or capacity should not be assumed to describe every detail of this version. Keep interior layout, carrying components and any included accessories tied to the selected offer.
The capacity number also cannot settle an airline size rule. The packed external measurements are a separate requirement, particularly if the bag will be used close to its full capacity.
A practical place on the shortlist
Consider the 42L when the backpack will carry the complete clothing load and you have identified a genuine need for its scale. Compare it with other main travel packs using that same load, then evaluate the carrying arrangement.
If you plan to use the bag for small daily outings after unpacking, consider that second role explicitly. A larger luggage choice may be right for transit while still leaving you wanting a separate compact day bag.
