TLDR: Harrow benefits more from building health rather than shields
Recently I’ve been seeing a fair amount of posts about harrow and how to build him. This post wont be a guide on how to build harrow in general, but rather my thoughts on building harrow for shields as a player who has played a lot of harrow and not just for eidolons.
When you first get harrow its definitely tempting to build for shields, after all his passive allows for the 2nd largest shield in the game and his 2nd ability penance scales duration on how much shield you consume. Much like many frames and descriptions, this sounds great on paper but falls off in execution. Lets give some examples:
Without any mods and full overshields harrow can get 40 seconds of duration on his 2nd ability. With redirection and full overshields that brings the number up to 57 seconds. Compare that to slotting a standard non-prime continuity which brings his maximum (without any other mods) penance duration to 62 seconds. This means running even common continuity is more efficient than trying to pump your shield up 440% with redirection.
Shields were reworked relatively recently within warframe’s life cycle allowing for shield gating. Shield gating gives you 1.3 seconds of invulnerability when damage occurs that would have broken your shield and gone into your health. However this can only occur once per full shield charge, so having a large shield makes shield gating more difficult to achieve consistently.
Finally armor and you. Shields get 25% damage reduction across the board but also cannot benefit from armor. Armor on the other hand provides damage reduction but only to health. Harrow has 175 armor at max rank, and according to the formula found on this page harrow naturally gets 36% damage reduction to his health without any armor boosting mods or effects.
Those 3 paragraphs sum up the idea on why i think you shouldn’t build harrow for shields, but as i mentioned those are all on paper stats so here are some real examples of those ideas put into practice
Not having a large shield means needing less enemies to hit with your 1st ability to fully charge it, thus maintaining shield gating more effectively and reducing how many times you need to cast it.
Harrow can already achieve a massive shield with just his base stats so building for duration in favor of shields will boost the duration of all of his abilities while still using your 1st ability to take advantage of a large shield pool.
Maintaining your 2nd ability is easier than casting your 1st into a group of enemies for surviving. You might have enough time to cast your 1st ability to save your hide, but swinging a well built melee into a crowd of enemies will fully restore your health in one hit no energy or casting time required.
Many players use adaptation on harrow. Relying on your 2nd ability to survive instead of a large shield pool allows you to not only effectively stack adaptation, but also benefit from armor damage reduction like the kind you get from arcane guardian.
I apologize for the long read, but there isnt really a succinct way to lay out all these thoughts. I hope this helps anyone aspiring to play more harrow.